Even as a majority of Crimeans voted in favour of joining Russia in a referendum, the US and its Western allies rejected the plebiscite as "illegal" and confronted Moscow.
Crimeans in Simferopol and Sevastopol celebrated, with official results Monday showed that 96.6 percent of the people were for joining Russia, the media reported.
The US and its allies rejected the referendum, calling the Sunday vote "illegal" and "contrary to Ukrainian constitution".
US President Barack Obama said the US would not recognise the Crimean referendum and vowed to impose fresh sanctions on Russia.
In his talks with Russian President Vladimir Putin over the phone, Obama said the vote in the Ukraine's autonomous republic violated the Ukrainian constitution, Xinhua quoted the White House as saying Sunday.
It was also held "under duress of Russian military intervention", Obama said.
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He told Putin that "Russia's actions were in violation of Ukraine's sovereignty and territorial integrity and that, in coordination with our European partners, we are prepared to impose additional costs on Russia for its actions".
Putin refused to back off.
"Putin said the Crimean population's vote is proceeding in full compliance with international law," the Kremlin web site said, citing the telephone conversation between the leaders.
"Russia will respect the choice of Crimean residents," Putin said, adding that he was concerned about the aggravation of the situation in eastern and southeastern regions of Ukraine.
But Putin and Obama agreed to continue searching for ways to restore stability in Ukraine.
Washington has canceled trade talks and military exchanges with Russia, and Obama has authorised visa bans and freezing of assets of some Russians and Ukrainians blamed for Moscow's military takeover of Crimea.
Putin told German Chancellor Angela Merkel earlier that Russia would "respect the choice" of the Crimeans.
Merkel, however, underscored the urgency of holding direct talks between Russia and Ukraine, a German government spokesperson said.
The German chancellor said the existing presence of the Organisation for Security and Cooperation in Europe (OSCE) in Ukraine should be quickly expanded.
She stressed that it was urgent and necessary for the governments of Russia and Ukraine to hold direct talks.
Washington and its allies have been pushing for Moscow to withdraw its military personnel posted in bases in Crimea, home to Russia's Black Sea Fleet, allow international monitors into Crimea and to open a dialogue with the Ukrainian government.
French Foreign Minister Laurent Fabius denied the legitimacy of Crimea's referendum, urging Russia to take immediate measures to avoid a "useless" and "dangerous" escalation of Ukrainian crisis.
"Nothing in the way that the referendum has been conducted should convince anyone that it is a legitimate exercise," British Foreign Secretary William Hague said.
The European Union said the referendum in Crimea was "illegal and illegitimate" and its outcome "will not be recognised".
Moscow Saturday vetoed a UN Security Council draft resolution while China abstained.
The resolution, drawn up by the US and backed by Western countries, called on international organisations to ignore the results of the voting in Crimea.
"China holds an objective and fair position on the Ukraine issue," Liu Jieyi, Chinese permanent representative to the UN, told the Security Council.
"The vote by the Security Council at this juncture will only result in confrontation and further complicate the situation," said Liu.
Crimea, historically part of the Russian Federation, was transferred to Ukraine in May 1954, then a republic of the Soviet Union.
In 1992, the Crimean Supreme Council (parliament) declared independence pending a referendum which was called off by the Ukrainian authorities.
Crimea held two other referendum in 1991 and 1994, testing voters' preference for greater autonomy within Ukraine or uniting with Russia.
The Crimean Supreme Council passed a resolution of declaration of independence March 11 this year to pave the way for Sunday's referendum.