With Ukraine and Russia seemingly on the brink of war, U.S. President Barack Obama has waded in warning Russia that it's "on the wrong side of history" in Ukraine and its actions violate international law.
Speaking to reporters at the White House on Monday, Obama said Washington is considering diverse economic and diplomatic options that could isolate Russia.
He, however, stressed the importance of de-escalating the situation.
Vice President Joe Biden has also urged Russia to pull its forces out of Ukraine.
In a phone conversation with Russian Prime Minister Dmitry Medvedev Monday, Biden called on Moscow to engage in dialogue with the Ukrainian government immediately.
The White House says Biden told the Russian premier that he supports the idea of deploying international monitors from the Organization for Security and Co-operation in Europe to cool tensions and mediate between the two sides.