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 Moscow could not ignore calls for help from Russian speakers, but that ties with the US should not be affected.
Crimean MPs have asked to join Russia and called a referendum on the move.
The Ukrainian Paralympic team has confirmed it will not boycott the Sochi Winter Paralympics.
The head of the team, Valeriy Sushkevich, said they would participate "so they remember us, remember Ukraine - a sovereign state, which sent its athletes here".
But he said: "If something major happens, Ukraine will leave the Games immediately".
The Games, which open in the Russian Black Sea resort later on Friday, has already been boycotted by many foreign dignitaries amid international tensions over Russia's military intervention in the southern Ukrainian region of Crimea.
During the hour-long phone conservation, Mr Obama told Mr Putin that Russia's actions 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 Russia could not "ignore calls for help and acts accordingly, in full compliance with international law".
But he also 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.
Ukraine's interim Prime Minister Arseniy Yatsenyuk said on Friday that Kiev was ready for talks with Russia, but Moscow must first withdraw its troops, abide by international agreements and halt "support for the separatists and terrorists in Crimea".
Washington on Thursday issued visa restrictions on a number of unnamed Ukrainian and Russian officials and individuals.
EU leaders in Brussels suspended talks with Moscow on easing travel restrictions on Russians entering the EU and warned of further measures if Moscow did not move to de-escalate the situation.
Russia's parliament said it supported the right of Crimea to hold a referendum on joining the Russian Federation.
Upper House speaker Valentina Matviyenko called it a "historic decision". "The Crimean parliament, as a legitimate authority, has... the sovereign right of the people to determine their future," she said.
The Crimean parliament on Thursday said it had decided "to enter into the Russian Federation with the rights of a subject of the Russian Federation" and asked President Putin "to start the procedure".
It plans to seek endorsement for the move in a referendum to the Crimean people on 16 March.
Mr Putin - who has the final decision - has not yet responded publicly to Crimea's request.
The US and EU joined the Ukrainian government in condemning Crimea's move as "illegitimate".
Ukraine's Interim President Olexander Turchynov cited Article 73 of the Ukrainian constitution which says issues relating to borders must involve a "referendum across the whole of 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 with more than 90 people killed in clashes with police.
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