• US Treasury hits Hamas with new sanctions.
• Charities and banks targeted.
• "Hamas should have nowhere to hide," says a top Treasury official.

The United States Treasury Department announced a new round of sanctions targeting Hamas' fundraising network Friday, the department's second attempt to block Hamas' money supply since the Oct. 7 terrorist attacks that killed 1,400 Israelis and saw another 200 Israelis taken hostage.

"A key reason for acting now is that we're seeing, in the wake of this month's attack, increased fundraising activity," said Brian Nelson, Treasury Under Secretary for Terrorism and Financial Intelligence, in an interview with CNBC Friday.

Nelson was in Saudi Arabia and Qatar this week, appealing for increased cooperation from Gulf countries, some of which maintain channels of communication with Hamas. Speaking from Doha, he said Treasury officials have stepped up their efforts to stop the money flow to Hamas in recent days. 

Deputy Treasury Secretary Wally Adeyemo was in London on Friday, where he laid out steps the United States and its partners are taking increase the financial pressure on Hamas.

"While Hamas itself has been under sanctions for decades, we must go after new, emerging shell companies, middlemen, and facilitators," he said.

"We are working with partners and allies around the globe to increase information sharing and collaboration to tackle terrorist financing," said Adeyemo. "Hamas should have nowhere to hide."

In addition to international cooperation, Adeyemo also emphasized the role of banks and cryptocurrency platforms in the overall sanctions campaign.

"Our expectation is that financial institutions and digital asset companies and others in the virtual currency ecosystem will take steps to prevent terrorists from being able to access resources," he said. "If they do not act to prevent illicit financial flows, the United States and our partners will."

Friday's new sanctions targeted several members of Iran's Revolutionary Guard who the United States said have been raising money for Hamas in various ways, including through two newly listed entities, "Islamic National Bank" and the "Al-Ansar Charity Association." 

The charity, "serves as a recruiting tool for terrorist activities," Treasury said in its sanctions announcement.

Sanctions designations were also issued against front companies in Turkey, Spain and Sudan.

"Don't expect this to be Treasury's last action," Matt Levitt, a former intelligence analyst at Treasury, told CNBC in an interview Friday.

A leading expert on terror financing at the Washington Institute for Near East Policy, Levitt testified twice on Capitol Hill this week about how Hamas gets its money, and what can be done to stop it.

He explained that while much of the focus in recent weeks had been on the global financial ties between Hamas and Iran, in reality the militant group gets most of its money by taxing and extorting money from people inside Gaza. 

But with Gaza under near constant air strikes since Oct. 7, hundreds of thousands of civilians displaced and commerce at standstill, there wasn't much money left for Hamas to access.

"Things are about to change for [Hamas]," said Levitt.

Following his speech in London, Adeyemo is headed to Brussels to meet with EU officials and continue the work of dismantling Hamas' financing networks.

One question for officials like Adeyemo and Nelson in the coming weeks will be how far the United States is willing to go to unilaterally to target Hamas financing.

While both of them emphasized that Washington is willing to act on its own if needed, they said the efforts are more effective with successful diplomacy and cooperation from governments and financial institutions. 

Levitt agreed, but said diplomacy can only go so far. He pointed to the fact that many previously sanctioned charities remain operational and under the direction of Hamas. The United States, he said, must be prepared to go further. 

"If the government and charitable organizations in Turkey aren't doing the right thing, the private sector in these countries must understand that anyone helping Hamas will be cut from the global financial system."