U.S. President Barack Obama hosts Ukraine's interim prime minister, Arseniy Yatsenyuk, at the White House Wednesday.
The White House says the president will stress his strong support for the Ukrainian people and talk about economic aid. The United States has already pledged $1 billion in aid to Ukraine.
U.S. Secretary of State John Kerry held another telephone call with Russian Foreign Minister Sergei Lavrov Tuesday on the ongoing situation in Ukraine.
A State Department spokeswoman said Kerry told Lavrov that it is "unacceptable" for Russian forces and "irregulars" to keep taking matters into their own hands in Ukraine. Kerry said the U.S. respects the fact that Russia has interests in Crimea, but added that it does not justify military intervention in the region, particularly the use of force.
The White House says there are no credible reports that the rights of ethnic Russians in Crimea and eastern Ukraine are being violated.
French Foreign Minister Laurent Fabius told France Inter radio Tuesday the West could impose sanctions against Russia as early as this week if Moscow does not work for calm in Crimea.
Also Tuesday, ousted Ukrainian president Viktor Yanukovych emerged to blame the interim government for Crimea's moves to break away from Ukraine. Mr. Yanukovych said he is still president and commander-in-chief. He called the interim leaders in Kyiv "extremists" and denounced the May 25 elections as illegal.
The Crimean regional legislature adopted a "declaration of independence" Tuesday with the intention of eventually becoming part of Russia. That question will be put to voters in a referendum Sunday. Ukraine's interim government and the West have dismissed the entire independence process in Crimea as illegitimate.
The crisis in Crimea began when Mr. Yanukovych fled Kyiv in February after three months of protests against his withdrawal from a European Union trade deal.
Most Crimean residents are ethnic Russians. Moscow has officially denied that its troops are participating in the occupation of Crimea; but, witnesses say military personnel in unmarked uniforms arrived in Russian-registered vehicles earlier this month and freely admit to being Russian.
( OPTIONAL SOUNDBITES
Ousted Ukrainian President Viktor Yanukovych :
"I declare that the elections for the president which are scheduled to be held on May 25 by a clique which seized power through an unconstitutional coup are absolutely illegitimate and illegal. They don't correspond to article 103 of Ukraine's constitution. Any organ of power that is formed as a result of those illegal elections will also be illegitimate and illegal."
"Ukraine is going through a difficult time now. Your actions have led to the fact that the Crimea is splitting off, that even at the point of a submachine gun, the population of the southeast is demanding respect for themselves and their rights."