The United States stands ready to "respond quickly" if a referendum on Crimea's defection to the Russian Federation is held as planned on Sunday, the White House has said.
Washington said it was "regrettable" that Russia had chosen not to act to reduce tensions in the Ukrainian region after US Secretary of State John Kerry held talks with Sergei Lavrov.
Mr Kerry has meanwhile tweeted a photo of his discussion with the Russian Foreign Minister, saying "many ideas" had been "put forward" during the six-hour talks.
John Kerry warned of "consequences" after his Russian counterpart made clear Moscow would respect the outcome of Crimea's referendum.
Foreign ministers meeting in Brussels will decide on Monday on sanctions for Russia if there is no de-escalation in Ukraine.
Crimea's new information minister has told ITV News that the planned referendum is no different to the situation in Scotland and Catalonia.