MOSCOW, Dec 9 (Reuters) - Russia accused the United States on Thursday of refusing to cooperate in a longstanding row 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 reaching an understanding on some "peripheral" issues, the two countries were deadlocked in the dispute over the size and working of their diplomatic missions. "Overall this whole bloc of issues is at a deep impasse and practically cannot be resolved because of the lack of U.S. cooperation," Ryabkov was quoted by Interfax news agency as saying. The U.S. and Russian embassies have come under staffing pressure as each side has cut the other"s representation in a series of tit-for-tat exchanges as bilateral relations have sunk to their worst point since the end of the Cold War. The Kremlin has said Putin proposed to Biden that the two countries should resolve the stand-off by lifting the staffing limits they had imposed. Tuesday"s call was dominated by tensions over Ukraine, with Biden voicing concern about a Russian military build-up near the border with its former Soviet neighbour and telling him Moscow would face serious economic consequences if it invaded. Putin has said talk of an invasion is "provocative" and accused Ukraine and NATO of fanning tensions. Biden said the next day he hoped for an announcement by Friday of high-level meetings with Russia and major NATO allies to discuss Moscow"s concerns and the possibility of "bringing down the temperature along the eastern front". Rybabkov described this as a "unilateral" statement, implying the U.S. side had not discussed it with Moscow. Asked if Russia would object to the participation of other NATO members, Kremlin spokesman Dmitry Peskov said: "We cannot say, because there is no understanding of how all this will be arranged."