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, theWhite 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, or complicit in, threatening the sovereignty and territorial integrity of Ukraine”.
EU leaders meeting in Brussels suspended talks with Moscow on easing travel restrictions on Russians entering the EU.
They said in a statement that if Russia did not move to de-escalate the situation, the EU would “decide on additional measures, such as travel bans, asset freezes and the cancellation of the EU-Russia summit”.
Russia’s parliament on Friday said it supported the request by Crimean MPs on Thursday to “enter into the Russian Federation with the rights of a subject of the Russian Federation”.
The Crimean parliament also said it would seek endorsement for the move in a referendum to the Crimean people on 16 March.
Mr Putin has not yet responded publicly to Crimea’s request.
The US and EU joined the Ukrainian government in condemning the move.
Ukraine’s Interim President Olexander Turchynov denounced the planned referendum as “illegitimate and unnecessary, it contradicts the will of the Ukrainian people”.
He cited Article 73 of the Ukrainian constitution which says issues relating to borders must involve a “referendum across the whole of Ukraine”.
Officials from Ukraine’s Paralympic delegation are expected to reveal whether the team will participate in the Games in a news conference at about 09:30 GMT on Friday.
Members of the team raised the Ukrainian flag and chanted “Peace for Ukraine” at a welcoming ceremony in Sochi on Thursday.
Ukrainian Paralympic Committee president Valeriy Suskevich made an emotional plea for peace. “My sportsmen dream about participating, but not without the Ukrainian people,” he said.
Several countries including the US and the UK have already pulled delegations out of the Games in response to Russia’s military’s movement inside Ukraine.
Pro-Russian gunmen moved in to seize strategic sites in Crimea, where the majority of the population is ethnic Russian, more than a week ago.
The authorities in Kiev and its Western allies suspect many of the gunmen are Russian troops, wearing unmarked uniforms, but this has been denied by Moscow.
The developments in Crimea began after Ukraine’s pro-Moscow president Viktor Yanukovych fled Kiev on 22 February following months of protests there.
The demonstrations – by Ukrainians seeking closer ties with the West – had turned violent days earlier more than 90 people killed in clashes with police.