The United States stopped the Russian government on Monday from paying holders of its sovereign debt more than $600 million from reserves held at U.S. 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 Feb. 24, foreign currency reserves held by the Russian central bank at U.S. financial institutions were frozen. But the 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...