What do we know so far about the mysterious crash of the helicopter carrying Iran's president?

The helicopter crash that killed Iran’s president and foreign minister has sent shock waves around the region.

Iranian state media on Monday said that President Ebrahim Raisi, the country’s foreign minister, Hossein Amirabdollahian, and others had been found dead after an hourslong search through a foggy, mountainous region of the country’s northwest. State TV gave no immediate cause for the crash.

Here’s what we know so far.

Who was on board and where were they going?

The helicopter on Sunday was carrying Raisi, Amirabdollahian, the governor of Iran’s East Azerbaijan province and other officials, according to the state-run IRNA news agency.

Raisi was returning after traveling to Iran’s border with Azerbaijan to inaugurate a dam with Azerbaijan’s President Ilham Aliyev when the crash occurred in the Dizmar forest in East Azerbaijan province.

IRNA said the crash killed eight people including three crew members aboard the Bell helicopter, which Iran purchased in the early 2000s.

How did the search operation go?

Iranian officials said the mountainous, forested terrain and heavy fog impeded search-and-rescue operations, which continued overnight.

The president of the Iranian Red Crescent Society, Pir-Hossein Koulivand, said Sunday evening that 40 search teams were on the ground despite “challenging weather conditions.” Because of the bad weather, it was "impossible to conduct aerial searches” via drones, Koulivand said, according to IRNA.

It was not until early Monday that officials announced the helicopter had been found and all of its occupants were dead.

How was the crash site found?

Early Monday, Turkish authorities released what they described as drone footage showing what appeared to be a fire in the wilderness that they “suspected to be wreckage of a helicopter.” The coordinates listed in the footage put the fire about 20 kilometers (12 miles) south of the Azerbaijan-Iranian border on the side of a steep mountain.

Footage released by IRNA showed what the agency described as the crash site, across a steep valley in a mountain range. Soldiers speaking in the local Azeri language said: “There it is, we found it.” Shortly after that, state TV in an on-screen scrolling text said: “There is no sign of life from people on board.”

How will Raisi's death impact Iran?

Raisi was seen as a protege to Iran’s supreme leader Ayatollah Ali Khamenei and a potential successor for his position within the country’s Shiite theocracy.

Under the Iranian constitution, if a president dies, the country’s first vice president — in this case, Mohammad Mokhber — becomes acting president, with elections mandated within 50 days. Khamenei has publicly assured Iranians that there would be “no disruption to the operations of the country” as a result of the crash.

What has international reaction been?

After news broke of the search operation, countries including Russia, Iraq and Qatar made statements of concern about Raisi’s fate and offered to assist in the search.

Azerbaijani President Aliyev offered any support necessary. Relations between the two countries have been chilly due to Azerbaijan’s diplomatic relations with Israel, Iran's regional arch-enemy.

Saudi Arabia, traditionally a rival of Iran although the two countries recently made a rapprochement, said it stands by "Iran in these difficult circumstances.”

There was no immediate official reaction from Israel. Last month, following an Israeli strike on an Iranian consular building in Damascus that killed two Iranian generals, Tehran launched hundreds of missiles and drones at Israel. They were mostly shot down and tensions have apparently subsided.

The U.S., which has its own history of tensions with Tehran, issued condolences in a State Department statement and added that "we reaffirm our support for the Iranian people and their struggle for human rights and fundamental freedoms.”