The United Nations says now is the time for "cool heads to prevail" in Ukraine, as Russian lawmakers approved President Vladimir Putin's request to send troops to Crimea.
Ukrainian Ambassador Yuriy Sergeyev told the Security Council Saturday that 15,000 Russian troops are already in Crimea under the pretense of protecting Russian citizens. He said Ukraine is calling on the U.N. to do everything possible to stop what he calls aggression against Ukraine.
Russian Ambassador Vitaly Churkin blamed the West for ratcheting up tensions in Ukraine and backing protests that ousted President Viktor Yanukovych.
He said Russia wants to know why last month's agreement between the opposition and Mr. Yanukovych to form a new coalition government was not implemented. He said Ukraine has to return to that deal and sideline those he calls radicals.
Churkin said President Putin has not yet decided whether to authorize a military force in Crimea. He said such a move would not be against Ukraine, but only on the territory of Ukraine to protect Russian lives.
The U.S. Ambassador to the U.N., Samantha Power, said Russian actions speak louder than words. She said a Russian force in Ukraine could push the situation beyond the breaking point and again called for international mediation in Crimea.
Meanwhile, the White House says President Barack Obama held a long telephone conversation with President Putin Saturday, expressing deep concern for what it calls the clear violation of Ukrainian sovereignty and international law.
The president said the United States is suspending participation in meetings to prepare for the G8 economic summit later this year in Sochi, Russia.
Russian news agencies say Mr. Putin told the president that Russia reserves the right to protect Russian speakers if there is violence in Crimea or eastern Ukraine.
Mr. Obama said such concerns must be brought up in direct negotiations with the Ukrainian government.
Acting Ukrainian President Oleksandr Turchynov said he has put the country's armed forces on combat alert. Prime Minister Arseniy Yatsenyuk is warning Russia that military intervention would mean war.
Ukraine has been describing what it says is an ongoing deployment of Russian troops in Crimea since Friday.
VOA correspondent Elizabeth Arrott says unidentified soldiers and military vehicles have appeared in Crimea, well beyond their local base. She said at least a dozen were stationed outside parliament in the Crimean capital of Simferopol on Saturday.
Crimea is a Black Sea peninsula placed under Ukrainian control in 1954 by then-Soviet leader Nikita Khrushchev. It became part of Ukraine when the Soviet Union collapsed in 1991. Crimea has a tiny border with Russia on its far eastern point. Most of the people living in Crimea are ethnic Russians, but the region also is home to ethnic Muslim Tartars who generally show disdain toward Russia.
Russia has said its troop movements in Crimea, where it leases a naval base in Sevastopol, conform to agreements with Ukraine.
Elsewhere, pro-Russian demonstrators fought with supporters of the new Ukrainian government in Ukraine's eastern city of Kharkiv Saturday. Pro-Russian demonstrations also erupted in other eastern cities.
Ukraine's troubles began in November when ousted president Yanukovych backed out of a trade deal with the European Union in favor of closer ties and economic aid from Russia.