The White House on Sunday rejected a referendum in Crimea, in which exit polls showed a majority of voters in the autonomous republic of Ukraine voted to rejoin Russia, threatening "increasing costs" for Russia for its " military intervention and violation of international law."

"We reject the 'referendum' that took place today in the Crimean region of Ukraine," spokesman Jay Carney said in a statement, adding the vote is contrary to Ukraine's constitution and the international community will not recognize the results of a poll "administered under threats of violence and intimidation from a Russian military intervention that violates international law."

Local television quoted an exit poll by the Crimean Republic Institute for Political and Social Studies as saying that 93 percent of voters in Crimea were in favor of reunification with Russia.

"No decisions should be made about the future of Ukraine without the Ukrainian government," Carney said, calling Russia's military intervention into Crimea and military exercises on Ukraine's eastern border "dangerous and destabilizing".

"As the United States and our allies have made clear, military intervention and violation of international law will bring increasing costs for Russia -- not only due to measures imposed by the United States and our allies but also as a direct result of Russia's own destabilizing actions," Carney added.

U.S. Secretary of State John Kerry on Thursday threatened "a very serious series of steps" against Russia with the European Union by Monday in response to Crimea's plebiscite.

A joint statement issued Sunday by European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso called the referendum in Crimea "illegal and illegitimate", saying its outcome "will not be recognized."

Russia has rejected Western calls for allowing international monitors into Crimea and for a dialogue with the Ukrainian government, which Moscow has dismissed as illegitimate.

Russian President Vladimir Putin told German Chancellor Angela Merkel on Sunday over the phone that the referendum does not breach international law and Russia will "respect the choice" of the Crimeans.

Russian Foreign Minister Sergei Lavrov confirmed Sunday to U.S. Secretary of State John Kerry via a telephone conversation that Moscow's position on Crimea referendum remained unchanged.

Lavrov urged the U.S. side to place its full influence on Kiev authorities to "stop mass lawlessness and arbitrariness against the Russian speaking population."

Russia, a permanent member of the UN Security Council, on Saturday vetoed a U.S.-sponsored draft resolution which would otherwise have declared the Crimean vote one with "no validity". It also noted that it would not adjust foreign policies over the recent tough statements by some Group of Eight (G8) countries.

Crimea, home to the Russian Black Sea Fleet and historically part of the Russian Federation, was transferred to Ukraine in May 1954, then a republic of the Soviet Union. Endite