A Russian attack on Ukraine is "still very much a possibility", but the human cost would be "immense", US President Joe Biden has said, BBC reports.
In remarks televised nationally, he said the US was ready to respond decisively to such a move.
The US president said Russia had now massed some 150,000 troops on the border with Ukraine.
Russia's defence minister has said some forces have withdrawn. Biden said that this had not been verified.
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would be good, but we have not yet verified that. We have not yet verified the Russian military units are returning to their home bases," the US president said."Indeed, our analysts indicate that they remain very much in a threatening position."
Biden's speech came hours after Russian President Vladimir Putin said Moscow's security concerns should be addressed and taken seriously.
Putin has always denied he is planning an incursion, and said Russia did not want another war in Europe. However, tensions have been rising since November.
