Russia on Thursday accused the United States of refusing to cooperate in a long-running dispute over their respective embassies, two days after the issue was raised in a call between Presidents Vladimir Putin and Joe Biden.

Deputy Foreign Minister Sergei Ryabkov said that despite having reached an understanding on some “peripheral” issues, the two countries were stuck in the dispute over the size and functioning of their diplomatic missions.

“In general, this whole bloc of issues is in a deep stalemate and practically cannot be resolved due to the lack of cooperation from the United States,” Ryabkov was quoted as saying by the Interfax news agency.

The U.S. and Russian embassies have come under pressure from staff as each side has cut off representation for the other in a series of coup exchanges, and bilateral relations have sunk to their worst since the end of the Cold War.

The Kremlin has said Putin proposed to Biden that the two countries resolve the confrontation by lifting the personnel limits they had imposed.

Tuesday’s call was dominated by tensions around Ukraine, as Biden raised concerns about the Russian military build-up near the border with its former Soviet neighbor and told him that Moscow would face serious economic consequences if it invaded.

Putin has called talking about an invasion a “provocation” and has accused Ukraine and NATO of stoking tensions.

Biden said the next day that he expected an announcement on Friday of high-level meetings with Russia and major NATO allies to discuss Moscow’s concerns and the possibility of “lowering the temperature along the eastern front.”

Rybabkov called this statement “unilateral”, implying that the US side had not discussed it with Moscow.

Asked whether Russia would oppose the participation of other NATO members, Kremlin spokesman Dmitry Peskov said: “We cannot say, because it is not known how all this will be organized”.

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