The United States stopped the Russian government on Monday from paying holders of its sovereign debt more than $600 million from reserves held at US banks, in a move meant to ratchet up pressure on Moscow and eat into its holdings of dollars.

Under sanctions put in place after Russia invaded Ukraine on February 24, foreign currency reserves held by the Russian central bank at US financial institutions were frozen.

But the US treasury department had been allowing the Russian government to use those funds to make coupon payments on dollar-denominated sovereign debt on a case-by-case basis.

On Monday, as the largest of the payments came due, including a $552.4 million principal payment on a maturing bond, the US government decided to cut off Moscow’s access to the frozen funds, according to a US Treasury spokesperson.

An $84 million coupon payment was also due on Monday on a 2042 sovereign dollar bond. The move was meant to force Moscow to make the difficult decision of whether it would use dollars that it has access to for payments on its debt or for other purposes, including supporting its war effort, the spokesperson said.

Russia faces a historic default if it chooses to not do so.

“Russia must choose between draining remaining valuable dollar reserves or new revenue coming in, or default,” the spokesperson said.

JPMorgan Chase & Co, which had been processing payments as a correspondent bank so far, was stopped by the US Treasury, a source familiar with the matter said.