This was CNBC's live blog tracking developments on the war in Ukraine. See here for the latest updates. 

Ukraine's capital Kyiv has been hit by another Russian air attack overnight, officials in the city said, noting that the latest strike was "exceptional" in its intensity and involved drones, cruise and probably ballistic missiles.

During the night, Kyiv's Mayor Vitali Klitschko reported a number of explosions in the city on his Telegram channel, saying falling rocket and drone debris had damaged buildings and cars in several of the city's districts, as well as started some fires.

In addition, a bright flash lit up the sky in Kyiv early Tuesday morning as the attack took place, video obtained by Reuters showed. The news agency said it was able to verify the location and date of the video but was unable to verify the cause of the flash.

The attack on Kyiv comes as a top Chinese envoy is set to begin a two-day visit to Ukraine on Tuesday as Beijing tries to position itself as a peace broker between Ukraine and Russia.

China's special representative on Eurasian affairs, Li Hui, is also set to visit Poland, France, Germany and Russia as part of Beijing's bid to foster talks "on a political settlement to the Ukraine crisis," its foreign ministry said last week.

Black Sea grain deal that reopened crucial Ukrainian ports set to expire this week

Russia has yet to decide if it will extend the terms of the Black Sea Grain Initiative, a deal that launched a humanitarian sea corridor for agricultural exports.

The deal is slated to expire on May 18.

Kremlin spokesman Dmitry Peskov told reporters that "there are still a lot of open questions" when asked about a potential extension of the agreement.

"When the appropriate decision is made, we will inform you, this is the only thing I can say so far," Peskov told reporters during a daily press briefing.

Read the full story here.

— Amanda Macias

Kremlin weighing Black Sea Grain Initiative extension

The Kremlin said that it has not yet decided to extend the Black Sea Grain Initiative, which is set to expire on May 18.

"When the appropriate decision is made, we will inform you, this is the only thing I can say so far," Kremlin spokesman Dmitry Peskov said.

"In general, the contacts continue. Basically, they're very concentrated now. You know that there are still a lot of open questions that relate to our part of the deal. We now have to make a decision," he added.

The Black Sea Grain Initiative eased Russia's naval blockade and saw the reopening of three key Ukrainian ports.

Since then, more than 900 ships carrying nearly 30 million metric tons of agricultural products have departed from Ukraine's war-weary ports.

Moscow previously said that the deal is one-sided and that it is not inclined to extend the current agreement.

— Amanda Macias

State Department aware of reports that U.S. citizen died in Bakhmut

The State Department said it was aware of reports that a U.S. citizen died in Bakhmut and is seeking additional information, a spokesperson confirmed to NBC News.

Wagner group chief Yevgeny Prigozhin appeared in a video Tuesday standing alongside a body he claimed was an American.

The spokesperson added that the State Department's ability to verify reports of deaths of U.S. citizens in Ukraine is extremely limited given the ongoing conflict. Since the war began last February, at least 10 U.S. citizens have been killed assisting Ukrainian forces.

"We offer our condolences to the families of all whose lives have been lost as a result of Russia's unprovoked and unjustified war against Ukraine," the State Department spokesperson said in a statement to NBC News.

"We reiterate our message that U.S. citizens should not travel to Ukraine due to the active armed conflict and the singling out of U.S. citizens in Ukraine by Russia's security officials and that U.S. citizens in Ukraine should depart immediately if it is safe to do so using any commercial or other privately available ground transportation options," the spokesperson added.

— Amanda Macias

One ship leaves Ukraine’s port of Odesa as expiration of Black Sea Grain Initiative looms

One ship carrying 62,000 metric tons of corn left Ukraine's ports of Odesa under the Black Sea Grain Initiative. The ship is destined for the Kingdom of Saudi Arabia.

Under the Black Sea Grain Initiative, which established a humanitarian sea corridor, more than 900 ships carrying 30 million metric tons of agricultural products have departed from Ukraine's war-weary ports. Russia has previously said that it would not recognize an extension of the deal, which is set to expire on May 18.

— Amanda Macias

Russia and Ukraine agree to meet African leaders over potential peace plan, South Africa's Ramaphosa says

Russian President Vladimir Putin and Ukrainian President Volodymyr Zelenskyy have agreed to meet with a delegation of African leaders for talks over a potential peace plan, South African President Cyril Ramaphosa said Tuesday.

In a joint press briefing alongside the Singaporean prime minister in Cape Town, Ramaphosa said Putin and Zelenskyy had expressed their willingness to receive a mission of African heads of state in both Moscow and Kyiv. This will include leaders of Zambia, Senegal, Congo, Uganda, Egypt and South Africa.

"Whether that will succeed or not is going to depend on the discussions that will be held," he added.

South Africa has come under fire for its staunch commitment to neutrality on the war in Ukraine, having hosted Russian Foreign Minister Sergei Lavrov in January and held a joint military operation with Russia and China in February.

- Elliot Smith

Ukraine lifts barriers to exports of some farm goods

Ukraine has removed barriers to the export of some agricultural commodities, imposed last year to prevent food shortages, in a bid to boost foreign currency income, its government said on Tuesday.

The country introduced export licences in 2022 to protect food supplies after agricultural production was hit by Russia's invasion. While licensing did not ban exports, it made them much more difficult.

The government said it would lift the requirement for export licences for live cattle, frozen cattle meat, chicken meat, eggs, rye, oats, millet and some other commodities.

It said via the Telegram messaging app that the resolution was developed in response to numerous requests from associations, and would "help to optimize agricultural exports and increase foreign exchange earnings for Ukraine".

The decision would not affect supply to the domestic market, the government said. Ukraine is a major producer of poultry meat and exporter of grain and cereals.

The European Union on May 2 set restrictions on imports of Ukrainian wheat, maize, rapeseed and sunflower seed to ease excess supply to Bulgaria, Hungary, Poland, Romania and Slovakia. Those states last week called for the curbs to be extended.

— Reuters

Ukraine hints update on fighter jets will come soon

Ukraine's Foreign Minister Dmytro Kuleba hinted Tuesday that the government would soon issue an update regarding the provision of modern fighter jets for Ukraine.

"Stay tuned for news — there will be even more soon, specifically regarding aircraft," Kuleba said on Facebook, in comments translated by news agency Ukrinform.

"Currently, intensive diplomacy is taking place at all levels, bringing us closer to effectively closing the Ukrainian airspace, significantly strengthening our Air Forces, and acquiring fundamentally new capabilities," Kuleba stated.

Kyiv has been asking its Western allies for fighter jets, with a specific desire for the U.S.' F-16s, for months but so far its international partners have been reluctant to donate fighter jets, citing logistical challenges and concerns it could antagonize Russia.

Kuleba said that he already has a rough understanding of the timeframe but did not disclose this.

Ukraine's President Volodymy Zelenskyy has visited Italy, Germany, France, and the U.K. in the last few days, looking to build a "jets coalition." The U.K. said it would help train Ukrainian pilots in the summer and would try to help Ukraine in such a coalition, but Prime Minister Rishi Sunak's spokesman said Monday that Britain has no plans to send fighter jets to Ukraine.

In any case, the spokesman said, the Ukrainian military indicated it would prefer to use F-16 fighter jets "and you will know the RAF don't use those," he said.

— Holly Ellyatt

Kremlin, on CIA video aimed at Russians, says our special services are monitoring

Commenting on a YouTube video encouraging Russians to make contact with the U.S. Central Intelligence Agency, the CIA, the Kremlin said on Tuesday that its own special services were tracking Western intelligence activity.

The short video in Russian, entitled "Why I made contact with the CIA: my decision", appeared on the CIA's official YouTube channel.

Kremlin spokesman Dmitry Peskov said he had not paid attention to it, but added: "I am convinced that our special services are monitoring this space in the necessary way."

He added: "We all know perfectly well that the CIA and other Western intelligence services are not reducing their activity on the territory of our country."

— Reuters

European leaders meet in Iceland to reaffirm values as Ukraine war rages on

European leaders are meeting in Iceland on Tuesday for a two-day summit meant to show their support for Ukraine but also send a powerful message on core democratic values many feel are under threat.

In only the fourth summit of the Council of Europe (CoE) since it was founded after World War Two, the 46 members of the leading human rights body, which is entirely separate from the European Union, will gather to discuss emerging threats as the war in Ukraine rages on.

"The Council of Europe is often underestimated in its importance," Frank Schwabe, a German lawmaker who was closely involved in the planning of the summit told Reuters.

The CoE's democratic values are upheld by the Strasbourg-based European Court of Human Rights, where citizens can take governments to court in case of human rights violations.

Russia's membership was suspended the day after it invaded Ukraine in February 2022. Moscow then left the watchdog hours before a vote to expel it.

According to a draft of the final declaration seen by Reuters, the leaders will approve a new Register of Damages, a mechanism to record and document evidence and claims of damage, loss or injury incurred as a result of the Russian invasion.

"The summit will also be about saying what happens if you don't respect the rules," Schwabe said. "The threat of expulsion is already a sharp sword. Even Russia didn't want to leave the Council of Europe, Turkey doesn't want to leave either."

Turkey, which is in the middle of a presidential election fought by President Tayyip Erdogan, faces removal from the CoE after it failed to implement a 2019 court ruling to release jailed businessman and philanthropist Osman Kavala.

The CoE's Committee of Ministers has launched infringement proceedings against Ankara that have so far stressed dialogue but could eventually see Turkey's removal or its membership suspended, experts say.

European leaders such as Germany's Olaf Scholz, Britain's Rishi Sunak and French President Emmanuel Macron will attend the summit in Reykjavik, while Ukraine's Volodymyr Zelenskiy will address his counterparts via videolink.

Icelandic organisers said the meeting will be an opportunity to support Ukraine through "concrete measures" as well as to boost initiatives to address emerging threats to democracy, including from climate change and artificial intelligence.

— Reuters

Pictures show Ukraine's emergency services at work in Kyiv

The State Emergency Service of Ukraine published images on its Facebook page Tuesday showing the services dealing with the aftermath of a large-scale drone and missile attack on Kyiv overnight.

The caption on the images is "Kyiv. May 16. Elimination of the consequences of another attempt by the enemy to attack the capital."

Ukrainian officials said the country was attacked from the north, east and south overnight with 18 missiles of various types, as well as attack drones. Ukraine's air defenses destroyed the missiles but falling debris caused damage to buildings and set several cars alight in some districts of Kyiv.

Ukraine's first lady meets with South Korea's Yoon

Ukraine's first lady, Olena Zelenska, met with South Korean President Yoon Suk Yeol as a special presidential envoy, South Korea's presidential office said on Tuesday.

Zelenska, the wife of Ukrainian President Volodymyr Zelenskyy, is visiting South Korea to participate in a media conference.

In an interview with South Korea's Yonhap news agency published on Tuesday, Zelenska expressed willingness to invite Yoon to her country, saying such a visit would be "very supportive" to Ukrainians.

She also warned against the risk of war fatigue and called for "more radical" support for Ukraine to fight against Russia's aggression.

South Korea, a major producer of artillery shells, has said it was not providing lethal weapons to Ukraine, citing its relations with Russia.

But Yoon said in an interview with Reuters last month his government might not "insist only on humanitarian or financial support" if civilians in Ukraine come under a large-scale attack or due to a "situation the international community cannot condone."

— Reuters

Ukraine attacked from three directions with various missiles, drones

Ukraine was attacked from the north, south and east overnight with 18 air, sea, and land-based missiles of various types, as well as attack drones, according to the leader of Ukraine's armed forces.

Six Kh-47M2 "Kinzhal" aeroballistic missiles were launched from six MiG-31K aircraft, nine Kalibr cruise missiles were launched from ships in the Black Sea, and three ballistic missiles were used to attack Ukraine, the head of Ukraine's armed forces, Valerii Zaluzhny, said on Telegram Tuesday morning.

He said all 18 missiles were destroyed by Ukraine's air defenses and air force. In addition, Russia attacked Ukraine with Iranian-made Shahed-136/131 drones, he said. CNBC was unable to verify the information in the post.

Officials in Kyiv described a massive attack on the capital overnight, saying the eighth attack on Kyiv since the start of May was "exceptional" in terms of the density of missiles used to attack it.

Preliminary information suggests at least three civilians were injured in the strikes, with falling debris from destroyed missiles and drones falling on cars and buildings in several districts in the city.

— Holly Ellyatt

The battle for Bakhmut is as hot as ever, UK defense ministry says

Despite recent Ukrainian claims of advances in the hotly contested town of Bakhmut in Donetsk, eastern Ukraine, the fighting there remains complex and intense, the U.K. noted Tuesday.

Britain's Ministry of Defense said the Wagner Group mercenary forces fighting in the town "continue to make gradual progress in clearing Ukrainian positions" in the town center, although it noted that over the last four days, Ukrainian forces made tactical progress stabilizing the flanks of Bakhmut to their advantage.

"As well as progress to the south of town, Ukrainian assaults have forced back the Russian frontline to the north-west of the town. This has likely enabled Ukrainian forces to re-establish more secure use of the key 0506 supply road," the ministry said in an intelligence update on Twitter.

Ukraine is holding Russia's western advances along the line of Donets-Donbas Canal, the U.K. noted, "turning the waterway into an obstacle as part of a deep defensive zone around the town of Chasiv Yar."

— Holly Ellyatt

Kyiv hit with massive, overnight air attack notable for its 'exceptional' density of missiles

Ukraine's capital Kyiv has been hit yet again by a Russian air attack overnight, officials in the city said, noting that the latest strike was "exceptional" in the number of weapons. They include drones, cruise and possibly ballistic missiles.

A bright flash lit up the sky in Kyiv early Tuesday morning as Russia carried out an overnight air attack on the city, video obtained by Reuters showed. The news agency said it was able to verify the location and date of the video but was unable to verify the cause of the flash.

During the night, Kyiv's Mayor Vitali Klitschko reported a number of explosions in the city on his Telegram channel, saying falling rocket and drone debris had damaged buildings and cars in several of the city's districts, as well as started some fires.

He warned civilians to stay in shelters and later posted on Telegram that three civilians had been injured, according to preliminary information.

Serhii Popko, head of the Kyiv city military administration, warned the city's residents to "head for cover" as air alerts sounded in the night in what marked the eighth air attack on the city since the start of May.

"This time, the enemy launched a complex attack from different directions simultaneously, using UAVs [drones], cruise missiles and probably ballistic missiles. It was exceptional in its density - the maximum number of attacking missiles in the shortest period of time," Popko said.

"According to preliminary information, the vast majority of enemy targets in the airspace of Kyiv were detected and destroyed," he added, saying more details on the number and type of missiles will soon be reported by Ukraine's air force.

China's envoy will begin Ukraine visit on Tuesday

A top Chinese envoy's visit to Ukraine is due to take place on Tuesday and Wednesday, according to media reports.

Li Hui, China's special representative for Eurasian affairs and former ambassador to Russia, will be visiting Ukraine, Russia and several other European cities in a trip Beijing says is aimed at discussing a "political settlement" to the Ukraine war, which China describes as a "crisis."

Reuters and NBC News both cited an unnamed Ukrainian government official as confirming the visit would begin Tuesday but declined to provide further details.

Ukraine's President Volodymyr Zelenskyy is in the U.K. on Monday to drum up more support for Kyiv ahead of its much-anticipated counteroffensive.

— Holly Ellyatt

White House set to announce additional sanctions for Iran's military support to Russia

The White House said it will impose additional sanctions targeting Iran as Washington ups the ante in its campaign against Tehran for supplying Moscow with weapons for its war on Ukraine. 

"In the coming days we will be announcing additional designations against those involved in the increased military trade between Russia and Iran," national security council spokesman John Kirby said on a call with reporters.

Kirby added that since August, Iran has provided Russia with more than 400 one-way attack unmanned aerial vehicles, or UAVs.

"By providing Russia with these UAVs, Iran has been directly enabling Russia's war of aggression in Ukraine," he added.

— Amanda Macias

Kremlin slams new weaponry for Kyiv but says it won't change the course of the war

The Kremlin said Monday that it takes a very dim view of the U.K.'s decision to provide more military hardware to Ukraine but claimed it wouldn't change the course of the war, or "special military operation," as it calls its invasion.

"We feel extremely negative about this," Kremlin press secretary Dmitry Peskov told reporters Monday, in comments translated by NBC News.

"The U.K. claims to be at the forefront among the countries that continue to pump weapons into Ukraine," he added.

The U.K. said last week that it will provide Storm Shadow long-range precision missiles to Ukraine, and on Monday it said it would give Kyiv hundreds of air defense missiles and long-range attack drones with a range of over 200 kilometers, or 124 miles.

The latest announcement came as Ukraine's Zelenskyy visited Britain, one of Kyiv's staunchest supporters.

Peskov downplayed the significance of the latest weaponry that's been announced for Kyiv, saying: "We repeat once again, this cannot have any significant and fundamental impact on the course of the special military operation, but, of course, it leads to further destructions, it leads to further retaliatory actions. That is, it makes this story much more difficult for Ukraine."

— Holly Ellyatt

UK has no plans to send fighter jets to Ukraine, PM's spokesman says

Britain has no plans to send fighter jets to Ukraine after the Ukrainian military indicated it would prefer to use F-16 fighter jets, Prime Minister Rishi Sunak's spokesman said on Monday.

Asked if Britain would send fighter jets to Ukraine, the spokesman said: "There are no plans to do that."

"The Ukrainians made the decision to train their pilots on F-16s and you will know the RAF don't use those," he said.

 — Reuters

UK and Ukraine discuss fighter jets, Zelenskyy says decision on the issue could come soon

Ukraine's President Volodymyr Zelenskyy said he and his British counterpart Rishi Sunak discussed the matter of fighter jets for Ukraine as they met in Britain on Monday, hinting that a decision could soon be made on the matter.

Kyiv has repeatedly asked its Western allies for fighter jets, saying they could make a big difference as it tries to reclaim Russian-occupied territory.

"We want to create a fighter jets coalition," Zelenskyy said Monday, following talks with Sunak, Reuters reported.

"I see that in the closest time, you will hear some, I think, very important decisions but we have to work a little bit more on it," he added.

As Zelenskyy's surprise visit to the U.K. was announced Monday morning, Downing Street issued a statement in which it said it would launch a training program for Ukrainian pilots in summer, saying "this will adapt the programme used by U.K. pilots to provide Ukrainians with piloting skills they can apply a different kind of aircraft."

This training, the government added, "goes hand in hand with U.K. efforts to work with other countries on providing F16 jets – Ukraine's fighter jets of choice."

The U.K. has previously ruled out giving Ukraine fighter jets, as has the U.S., but the latest comments signal a change of position could be on the cards.

– Holly Ellyatt

UK set to give more aid to Ukraine as Zelenskyy visits Britain

Britain's Prime Minister Rishi Sunak has welcomed his Ukrainian counterpart Volodymyr Zelenskyy to his countryside residence in a surprise visit by the president.

The British government is expected to "confirm the further U.K. provision of hundreds of air defence missiles and further unmanned aerial systems including hundreds of new long-range attack drones with a range of over 200km," or 124 miles.

"These will all be delivered over the coming months as Ukraine prepares to intensify its resistance to the ongoing Russian invasion," Downing Street said in a statement.

During their meeting today at the prime minister's official countryside residence Chequers, Sunak will discuss with Zelenskyy what support Ukraine needs from the international community, both in terms of immediate military equipment and long-term defenses, the government said.

Zelenskyy's trip to today comes after the Ukrainian president's tour of several European capitals in recent days as he tries to win more military support ahead of the country's much-vaunted counteroffensive in Ukraine.

"This is a crucial moment in Ukraine's resistance to a terrible war of aggression they did not choose or provoke," Sunak said in a statement.

"We must not let them down. The frontlines of Putin's war of aggression may be in Ukraine but the fault lines stretch all over the world. It is in all our interest to ensure Ukraine succeeds and Putin's barbarism is not rewarded," he added.

The U.K. is one of Ukraine's largest military supporters, providing masses of military hardware including armored vehicles, tanks and ammunition as well as training to thousands of Ukrainian soldiers. The U.K. said it had provided £2.3 billion ($2.9 billion) worth of military support to Ukraine in 2022 — more than any country other than the U.S.

Last week, the U.K. donated long-range Storm Shadow precision missiles to Ukraine which it said could be "critical in helping the country defend against the relentless bombardment of their critical national infrastructure."

The government also hinted it could be galvanizing support among Ukraine's allies to get fighter jets to Kyiv after repeated requests by Ukraine.

Britain will launch "an elementary flying phase for cohorts of Ukrainian pilots to learn basic training" this summer and said "this will adapt the programme used by U.K. pilots to provide Ukrainians with piloting skills they can apply a different kind of aircraft."

"This training goes hand in hand with U.K. efforts to work with other countries on providing F16 jets – Ukraine's fighter jets of choice," the government said.

— Holly Ellyatt

Read CNBC's previous live coverage here:

China set to visit Ukraine; 8,800 civilians killed in Russian invasion so far, UN says