US President Barack Obama has urged Russia's Vladimir Putin to seek a diplomatic solution to the crisis in Ukraine, in a lengthy telephone call.
The Russian president told Mr Obama ties between their two countries should not suffer because of disagreements over Ukraine, the Kremlin said.
A move by Crimean MPs to seek union with Russia has heightened tensions.
The Ukrainian Paralympic team is set to decide whether it is participating in the Sochi Winter Paralympics.
The Games, which opens in the Russian Black Sea resort later on Friday, has already been boycotted by many foreign dignitaries.
During the hour-long phone conservation, Mr Obama told Mr Putin that Russia's actions in Crimea were a violation of Ukrainian sovereignty, the White House said in a statement.
He said there was a solution available that suited all parties, involving talks between Kiev and Moscow, international monitors in Ukraine and Russian forces returning to their bases.
For his part, President Putin said US-Russian 'relations should not be sacrificed due to disagreements over individual, albeit extremely significant, international problems,' the Kremlin said.
It was the two leaders' second telephone call concerning Ukraine in less than a week.
Earlier on Thursday, Washington issued visa restrictions on a number of unnamed Ukrainian and Russian officials and individuals 'to deny visas to those responsible for, o.