The United States will send nearly 3,000 extra troops to Poland and Romania to shield Eastern Europe from a potential spillover from the crisis over the massing of Russian troops near Ukraine, U.S. officials said on Wednesday.

Russia has denied plans to invade Ukraine but signaled it was in no mood for compromise on Wednesday by mocking Britain, calling Prime Minister Boris Johnson "utterly confused" and accusing British politicians of "stupidity and ignorance."

Moscow has deployed more than 100,000 troops near Ukraine's borders and says it could take unspecified military measures if its demands are not met, including a promise by NATO never to admit Kyiv.