U.S. escalates sanctions with a freeze on Russian central bank assets.

The Treasury Department on Monday moved to further cut off Russia from the global economy, announcing that it would immobilize Russian Central Bank assets that are held in the United States and impose sanctions on the Russian Direct Investment Fund, a sovereign wealth fund that is run by a close ally of President Vladimir V. Putin.

The moves are meant to curb Russia’s ability to use its war chest of international reserves to blunt the impact of sanctions that the United States and European allies have enacted in response to Russia’s invasion of Ukraine.

“The unprecedented action we are taking today will significantly limit Russia’s ability to use assets to finance its destabilizing activities, and target the funds Putin and his inner circle depend on to enable his invasion of Ukraine,” Treasury Secretary Janet L. Yellen said in a statement.

Russia has spent the last several years bolstering its defenses against sanctions, amassing $643 billion in foreign currency reserves in part by diverting its oil and gas revenues. New restrictions by the United States and its allies against selling rubles to Russia aim to undercut the country’s ability to support its currency in the face of new sanctions on its financial sector.

As a result of the sanctions, Americans are barred from taking part in any transactions involving the Russian Central Bank, Russia’s National Wealth Fund or the Russian Ministry of Finance.

Any Russian central bank assets that are held in U.S. financial institutions are now stuck and financial institutions outside the United States that hold dollars for the Russian central bank cannot move them. Because the United States has acted in coordination with European allies, Russia’s ability to use its international reserves to support its currency has been curbed.

It is not clear how much of Russia’s currency reserves are held in U.S. dollars, and Biden administration officials declined to provide an estimate in a briefing with reporters on Monday.

Senior Biden administration officials said the actions were effective immediately. They noted that the value of Russia’s ruble had already fallen more than 30 percent over the weekend and that Russia’s central bank more that doubled its interest rate to try to mitigate the fallout. They also predicted that inflation would soon spike and economic activity would contract as the country’s currency lost value.

The moves represent a significant escalation of U.S. sanctions, although the Treasury Department said it was making an exemption to ensure that transactions related to Russia’s energy exports can continue. It is issuing a “general license” to authorize certain energy-related transactions with the Russian Central Bank.

The carve-out means that energy payments will continue to flow, mitigating risks to global energy markets and Europe, which is heavily reliant on Russian oil and gas exports. U.S. officials said that they want energy prices to remain steady and that they do not want a spike in prices to benefit Mr. Putin, however they noted that they are considering measures that would restrict Russia from acquiring technology it needs to be an energy production leader in the long term.

On Saturday, the European Commission, Britain, Canada, France, Germany, Italy and the United States said they would remove some Russian banks from the SWIFT financial messaging system, essentially barring them from international transactions, and impose new restrictions on Russia’s Central Bank to prevent it from using its large international reserves to sidestep sanctions.

Biden administration officials said on Monday that the full list of Russian banks that are being cut off from SWIFT is still being finalized in coordination with European countries.