Russian President Vladimir Putin said in a phone conversation with U.S. President Barack Obama that "Russia reserves its right to protect its interests" in Ukraine's Crimea, as Russian troops took over the peninsula on Saturday, and after parliament granted Putin approval to invade Ukraine.
Obama told Putin that Russia had committed a clear violation of Ukrainian sovereignty by sending forces into Crimea and warned of consequences.
"The United States condemns Russia's military intervention into Ukrainian territory," the White House said in a statement outlining what was discussed in a 90-minute phone call between Obama and Putin.
Putin's open assertion of the right to send troops to a country of 46 million people on the ramparts of central Europe creates the biggest confrontation between Russia and the West since the Cold War.
Troops with no insignia on their uniforms but clearly Russian - some in vehicles with Russian number plates - have already seized Crimea, an isolated peninsula in the Black Sea where Moscow has a large military presence in the headquarters of its Black Sea Fleet. Kiev's new authorities have been powerless to stop them.
Ukrainian Prime Minister Arseny Yatseniuk, leading a government that took power after Moscow's ally Viktor Yanukovych fled a week ago, said Russian military action "would be the beginning of war and the end of any relations between Ukraine and Russia".
The United States and Canada said they are recalling their ambassadors to Russia for consultations about the crisis in Ukraine and are freezing preparations to take part in the Group of Eight summit in Sochi.
Canadian Prime Minister Stephen Harper, who talked earlier in the day with U.S. President Barack Obama, said Canada condemned Russia's intervention in Ukraine in the strongest possible terms.
As the Russian forces solidified their control of Crimea unrest spread to other parts of Ukraine on Saturday. Pro-Russian demonstrators clashed, sometimes violently, with supporters of Ukraine's new authorities and raised the Russian flag over government buildings in several cities.
"This is probably the most dangerous situation in Europe since the Soviet invasion of Czechoslovakia in 1968," said a Western official on condition of anonymity. "Realistically, we have to assume the Crimea is in Russian hands. The challenge now is to deter Russia from taking over the Russian-speaking east of Ukraine."
Ukraine's ambassador to the United Nations asked an emergency session of the Security Council on Saturday "to do everything possible now" to stop Russian "aggression" as Russian troops took over the strategic Crimea region.
Calling the situation in Ukraine "as dangerous as it is destabilizing," U.S. Ambassador to the UN Samantha Power told the council, "It is time for the Russian military intervention in Ukraine to end."
Power and other members of the council called for sending international monitors to Ukraine as soon as possible to observe the situation, and Power warned that "Russia's provocative actions could easily push the situation beyond the breaking point." She also mentioned work on an international mediation mission to send to Ukraine.
The Security Council met in emergency session for the second straight day on the rapidly developing events in Ukraine. It met briefly in an open, televised session, despite initial objections from Russia, then resumed meeting behind closed doors.
The council took no action. As a permanent member of the council, Russia has veto power and can block the UN's most powerful body from adopting any resolution criticizing or sanctioning Moscow.
Defense Secretary Chuck Hagel told his Russian counterpart Sergei Shoigu in a phone call that Moscow's military intervention risked creating further instability and an escalation "that would threaten European and international security", the Pentagon said. A U.S. defense official said there had been no change in U.S. military posture or in the alert status of forces.
EU foreign affairs chief Catherine Ashton urged Moscow not to send troops. Swedish Foreign Minister Carl Bildt said this would be "clearly against international law". Czech President Milos Zeman likened the crisis to the 1968 invasion of Czechoslovakia.
"Urgent need for de-escalation in Crimea," tweeted NATO Secretary-General Anders Fogh Rasmussen. "NATO allies continue to coordinate closely."
NATO ambassadors will meet in Brussels on Sunday to discuss the situation, Rasmussen tweeted. "North Atlantic Council will meet tomorrow followed by NATO-Ukraine Commission," he wrote.
Putin said his request for authorization to use force in Ukraine would last "until the normalization of the socio-political situation in that country". His justification - the need to protect Russian citizens - was the same as he used to launch a 2008 invasion of Georgia, where Russian forces seized two breakaway regions and recognized them as independent.
In a statement posted online, the Kremlin said that in his phone call with Obama, Putin "underlined that there are real threats to the life and health of Russian citizens and compatriots on Ukrainian territory".
France, Britain and Germany issued calls for de-escalation in Crimea hours after U.S. President Barack Obama warned that military intervention in the region would be deeply destabilizing and "carry costs".
British Prime Minister David Cameron said he had told Russian President Vladimir Putin in a phone call on Friday that "there can be no excuse for outside military intervention in Ukraine".
"Everyone must think carefully about their actions and work to lower, not escalate, tension," he said. "The world is watching."
French President Francois Hollande spoke to Putin on Saturday to tell him of his "grave concern" and urge him to "avoid any use of force and to seek a solution to the crisis with the international community", a statement from Hollande's office said.
Hollande urged European countries to take swift and decisive action to find a way out of the crisis in Crimea when their foreign ministers meet in Brussels on Monday.
"Everything must be done to avoid outside intervention and the risk of a highly dangerous escalation," his office said.
Hollande also spoke about the situation in Crimea with U.S. President Barack Obama, German Chancellor Angela Merkel and European President Herman Van Rompuy.
No bloodshed followed Yanukovych's overthrow, but Ukraine's new leadership faces a challenge in Crimea, which was part of Russia until 1954.
'War has arrived'
On Kiev's central Independence Square, where protesters camped out for months against Yanukovych, a World War Two film about Crimea was being shown on a giant screen, when Yuri Lutsenko, a former interior minister, interrupted it to announce Putin's decree. "War has arrived," Lutsenko said.
Hundreds of Ukrainians descended on the square chanting "Glory to the heroes. Death to the occupiers."
Although there was little doubt that the troops without insignia that have already seized Crimea are Russian, the Kremlin has not yet openly confirmed it. It described Saturday's authorisation as a threat for future action rather than confirmation that its soldiers are already involved.
A Kremlin spokesman said Putin had not yet decided to use force, and still hoped to avoid further escalation.
In Crimea itself, the arrival of troops was cheered by the Russian majority. In the coastal town of Balaclava, where Russian-speaking troops in armored vehicles with black Russian number plates had encircled a small garrison of Ukrainian border guards, families posed for pictures with the soldiers. A wedding party honked its car horns.
"I want to live with Russia. I want to join Russia," said Alla Batura, a petite 71-year-old pensioner who has lived in Sevastopol for 50 years. "They are good lads... They are protecting us, so we feel safe."
But not everyone was reassured. Inna, 21, a clerk in a nearby shop who came out to stare at the armored personnel carriers, said: "I am in shock. I don't understand what the hell this is... People say they came here to protect us. Who knows? ... All of our (Ukrainian) military are probably out at sea by now."
The rapid pace of events has rattled the new leaders of Ukraine, who took power in a nation on the verge of bankruptcy when Yanukovych fled Kiev last week after his police killed scores of anti-Russian protesters in Kiev. Ukraine's crisis began in November when Yanukovych, at Moscow's behest, abandoned a free trade pact with the EU for closer ties with Russia.
For many in Ukraine, the prospect of a military conflict chilled the blood.
"When a Slav fights another Slav, the result is devastating," said Natalia Kuharchuk, a Kiev accountant.
"God save us."
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