President Obama calls the deployment of Russian troops in Ukraine's Crimean region a clear violation of international law.
In a statement at the White House, Obama said the U.S. and allies are moving forward together to impose sanctions on Russia.
He said the new government of Ukraine is legitimate and must be respected.
Obama got the ball rolling on sanctions with an executive order targeting individuals or entities involved in what he called "undermining the democratic processes or institutions in Ukraine."
Meantime, the State Department will impose visa restrictions on a number of officials and individuals who may have been complicit in threatening the sovereignty of Ukraine.