Election authorities in the breakaway Ukraine region of Crimea say 95 percent of voters support secession and a move to join Russia. The data was announced late Sunday with half of the referendum ballots counted. Voter turnout was placed at between 75 and 80 percent.
The tally came as the peninsula's pro-Moscow leader, Sergei Aksyonov, announced that his government will formally apply on Monday to join the Russian Federation.
In Kyiv, Ukraine's interim Prime Minister Arseniy Yatsenyuk - speaking at an emergency cabinet meeting - called the Moscow-backed Crimea vote "a circus spectacle" directed at gunpoint by Russia. He spoke as thousands of heavily armed Russian troops patrolled major cities on the peninsula as voters cast ballots.
Shortly after the polls closed, the White House released a statement saying it rejects the referendum. It said the international community will not recognize the results of a poll taken under threats of violence and intimidation from a Russian military intervention that violates international law.
It said no decision should be made about the future of Ukraine without the Ukrainian national government.
The statement also said the presidential elections planned for May 25 will provide a legitimate opportunity for all Ukrainians to make their voices heard on the future of their country.
A top White House aide repeated Western warnings of economic sanctions against Moscow if secession occurs.
The European Union and the European Council also released statements Sunday calling the referendum illegal and illegitimate, and warning that its outcome will not be recognized internationally.
Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on Sunday agreed to push for Ukrainian constitutional reforms for power sharing and decentralization as a solution to the crisis.
In Kyiv, Ukraine's acting defense minister told reporters that both Ukraine and Russia have agreed on a truce in Crimea until March 21.
Defense Minister Ihor Tenyukh said the agreement covers Russia's Black Sea fleet, which is stationed in Crimea. He also said no measure will be taken against Ukrainian military facilities during the truce, and that Ukraine's military sites -- blockaded for days -- are now replenishing their supplies.
Sunday's vote came a day after Russian forces seized a natural gas facility just outside Crimean territory. The Ukrainian Foreign Ministry called the move "a military invasion by Russia."
Ukraine provides the peninsula with all of its water and energy needs, and some analysts say the seizure may be aimed at ensuring the peninsula's energy requirements are met in the event Kyiv were to cut off supplies.
Crimea is a primarily ethnic-Russian region within Ukraine. Moscow says it has the right to protect the interests of ethnic Russians in Crimea.
Ukraine's Foreign Ministry said Saturday Russian forces have seized the Ukrainian village of Strilkove, near the Crimean border.
There are no reports of shots being fired, but the ministry called the takeover an "invasion" and demands that Russian soldiers leave. Ukrainian border guards say the Russians are guarding a gas pumping station in the town.
Meanwhile, White House Spokesman Jay Carney on Sunday promised a swift response to any additional Russian advances into Ukraine.
“There most definitely will be additional costs if Russia escalates this conflict rather than de-escalates. And they will be imposed by the United States, but also by our European partners,” Carney said.