President Barack Obama has warned the United States is planning a string of economic and diplomatic sanctions to "isolate" Russia if it does not reverse its incursion into Ukraine.
"Russia is on the wrong side of history," Obama said, declaring that the world was all but united in viewing Moscow's dispatch of troops to Crimea as a violation of international law.
A day before Secretary of State John Kerry arrives in Kiev to show US backing for Ukraine's right to chart its own future, Washington expanded on the "costs" Russia may have to pay for its action.
It pointed to the sharp decline of the ruble as evidence Russia was already paying a heavy price and Obama asked Congress to put an economic support package for Ukraine on the top of its agenda.
"What cannot be done is for Russia, with impunity, to put its soldiers on the ground and violate basic principles that are recognised around the world," Obama said.
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"What we are also indicating to the Russians is that if, in fact, they continue on the current trajectory that they're on, that we are examining a whole series of steps - economic, diplomatic - that will isolate Russia."
Obama said that after his round of calls to European leaders he was convinced the world was "largely united" in the belief that Russia had violated Ukraine's territorial integrity and international law.
At the State Department, spokeswoman Jennifer Psaki said Washington was prepared to "move forward" on sanctions against Russia and that US calls for action were already having an impact.
"If you look at the sharp decline of the Russian ruble, if you look at the Russian stock market today, those are just two examples," she said.
Psaki said there was no time-frame yet for when the United States could impose sanctions, but added "we're looking at a broad range of options, whether that's individuals, whether that's institutions, whether that's officials, those are all under consideration."
Possible options include visa bans or asset freezes on members of Russia's political and financial elite. Steps could also be taken against some Russian financial institutions.
Obama hinted that after already suspending co-operation with Russia on G8 matters, US partners would boycott the group's summit in the Russian resort of Sochi in June.
In another show of US anger, the White House took the symbolic step of announcing that Washington would not send an official delegation to the Winter Paralympics, which begin in Sochi on Friday.
US athletes however will still take part.
