Russia has become even more isolated after 12 of Vladimir Putin's UN team were booted out of the US.
The United States has expelled the group of Russian diplomats over national security concerns, U.S. and Russian diplomats said.
The U.S. mission to the United Nations described the Russian diplomats as "intelligence operatives" who had been "engaging in espionage activities that are adverse to our national security".
"This action has been in development for several months," said U.S. mission spokesperson Olivia Dalton.
Russia's U.N. Ambassador Vassily Nebenzia told reporters the diplomats had been asked to leave by March 7.
He said Russia would respond to the move "because it's diplomatic practice."
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Nebenzia then raised the issue at the start of a U.N. Security Council meeting on the humanitarian situation in Ukraine, describing the U.S. move as "hostile" and a violation of its commitments as host of the U.N. headquarters in New York.
U.S. Deputy U.N. Ambassador Richard Mills responded: "Those diplomats that have been asked to leave the United States were
engaged in activities that were not in accordance with their responsibilities and obligations as diplomats."
He said they had been asked to leave "so they do not harm the national security of the host country," adding that the decision was taken in full accordance with the U.N. headquarters agreement.
The United States and its allies have already slapped sweeping economic sanctions on Moscow for its attack on Ukraine - the biggest assault on a European state since World War Two - and moved to ramp up military and other assistance.
It comes as Russia faces deepening isolation and economic turmoil as Western nations, united in condemnation of its assault, attempt to cripple it with an array of sanctions.
Ukraine's allies also increased weapons transfers in support, with Finland agreeing to ship 2,500 assault rifles and 1,500 anti-tank weapons.
Putin's war has rumbled into its second week but things are not quite going to plan.
The Russian President and former KGB agent is understood to have been left "humiliated" after his goal to conquer his neighbours in 48 hours failed.
Instead, his troops have been met with a plucky and brutal resistance, suffering their share of heavy losses on the ground despite moving in on Kyiv rapidly.
The capital, as well as Kharkiv and Zhytomir, are under continued air strikes this evening as the first round of peace talks ended.
The two sides met on the Belarusian border while invading forces clashed with opposing troops and civilians on a fifth day of conflict.
In a worrying sign, Russia's defence ministry said its nuclear missile forces and Northern and Pacific fleets had been placed on enhanced combat duty.
Ukrainian President Volodymyr Zelensky, meanwhile, has said this evening he has signed a request to join the European Union, urging members to fast track the country on board.
