US Vice-President Joe Biden warned on a visit to Kiev Friday that Russia risked further isolation over its "unacceptable" aggression in Ukraine.
"It's simply unacceptable in the 21st century for countries to attempt to redraw borders by force... because they don't like a decision their neighbour has made," he said after meeting Ukrainian President Petro Poroshenko.
He warned that Russia had failed to fulfil its commitments under agreements struck in September, adding: "So long as that continues, Russia will face rising costs, greater isolation."
Moscow denies offering military support to separatists locked in a struggle for territory in eastern Ukraine but the West accuses Russia of involvement, sending diplomatic relations to a post-Cold War low.
Ukraine's leaders had hoped Biden would use his visit to announce further US assistance for its forces in the east.
The US has so far limited its security support to non-lethal assistance but Kiev wants it to go further and offer weapons and ammunition.
Biden made no direct mention of increasing assistance to Ukraine during the press conference.
But a statement from his office said that the White House was pledging a further $20 million (16 million euros) to support reforms in law enforcement and justice, plus $3 million more for food rations and displaced people.
That brings to nearly $320 million it has committed this year.