US Secretary of State Antony Blinken has accused Russia of trying to divide Ukrainian society, as fears mount of a Russian invasion of Ukraine.
An estimated 100,000 Russian troops have been deployed near Ukraine's borders and Mr Blinken, visiting Kyiv, said Russia could launch an attack at very short notice.
Mr Blinken also promised "relentless" diplomacy to stop Russian aggression.
Russia has repeatedly denied planning to invade its neighbour.
At a news conference with the Ukrainian foreign minister, Mr Blinken accused Russia of trying to weaken Ukraine's diplomatic institutions and to divide Ukrainian society, "using everything from election interference to disinformation to cyber attacks".
He also pledged "relentless diplomatic efforts to prevent renewed aggression and to promote dialogue and peace", and repeated a warning of tough sanctions against Russia in the event of an invasion.
Mr Blinken will meet his Russian counterpart in Geneva on Friday, after talks with European allies in Berlin.
