US President Barack Obama warned on Monday that most of the world believes that Russia has violated international law by intervening in Ukraine.
The American leader said Moscow had put itself "on the wrong side of history" by mobilizing forces within Ukraine after the country's pro-Russian president was ousted in a popular revolt.
"I think the world is largely united in recognizing the steps Russia has taken are a violation of Ukranian sovereignty ... a violation of international law," Obama said.
Ukraine's new westward-leaning government has accused Russia of mounting a de facto invasion by deploying troops on Ukrainian soil in the Crimean peninsula.
But Moscow protests it may be forced to act to protect ethnic Russians in Ukraine amid the chaos following the uprising against fugitive former president Viktor Yanukovych.
Western powers are mulling sanctions to punish Russia for its intervention.
Obama said he had told Russia that "if in fact they continue on the current trajectory, that we are examining a whole series of steps -- economic, diplomatic -- that will isolate Russia."