The White House says President Barack Obama has told his Russian counterpart, Vladimir Putin, that Moscow's actions in Ukraine are a violation of that country's sovereignty and territorial integrity.
Officials say the two leaders spoke for an hour on the telephone Thursday. It is their first known direct contact since Saturday, shortly after Russian forces took control in Ukraine's Crimean peninsula.
The White House says Mr. Obama told the Russian leader there still is a way to resolve the dispute diplomatically. He said this would entail Russian forces moving back to their base in Crimea; the governments of Ukraine and Russia holding direct talks, and international monitors getting access to ensure that the rights of ethnic Russians in Ukraine are protected.
Earlier in the day, Mr. Obama said a March 16 referendum decreed by pro-Russian lawmakers on the future of Ukraine's Crimea peninsula violates international law and Ukraine's constitution.
Speaking at the White House Thursday, Mr. Obama said any discussion about Ukraine's future "must include the legitimate government of Ukraine."
As political uncertainty gripped Crimea Thursday, the U.S. president also signed an executive order authorizing sanctions on those found to have stolen assets of the Ukrainian people or to have violated Ukraine's territorial integrity. His order includes visa restrictions and also blocks the transfer from the United States of assets belonging to anyone who has undermined democratic institutions in Ukraine. It does not name targeted individuals.
On Capitol Hill, the House of Representatives voted to provide loan guarantees of $1 billion to Ukraine. It's a fraction of the Ukrainian government's request, but is the first tangible congressional action. The measure now goes to the Senate.
Mr. Obama said the sanctions were imposed in "close coordination" with America's European allies.
"In 2014 we are well beyond the days when borders can be redrawn over the heads of democratic leaders," Mr. Obama said.
Earlier, the European Union voted to freeze the assets in Europe held by 18 Ukrainians, including ousted president Viktor Yanukovych, former premier Mykola Azarov and 16 former ministers, businessmen and security chiefs. Mr. Yanukovych's two sons and Mr. Azarov's son also were targeted.
The EU, facing what its leaders say is the the continent's greatest security challenge since the Balkan wars, also is suspending visa talks with Moscow.