"We are going home. Crimea is in Russia," Crimea's Prime Minister Sergey Aksyono

With 75% percent of the ballots counted, close to 96% of voters want to become part of that country, according to the Crimean Electoral Commission. An official had announced earlier that more than 80% of voters had cast ballots by the time polls closed at 8 p.m. local time (2 p.m. ET) Sunday.

"We are going home. Crimea is in Russia," Crimea's Prime Minister Sergey Aksyonov told crowds celebrating in Simferopol's Lenin Square. Music blared as they cheered and waved Russian flags.

The United States has already said it expects the Black Sea peninsula's majority ethnic Russian population to vote in favor of joining Russia. Moscow has strongly backed the referendum.

U.S. President Barack Obama and Russian President Vladimir Putin spoke Sunday, according to a readout from the White House.

"President Obama emphasized that the Crimean 'referendum,' which violates the Ukrainian constitution and occurred under duress of Russian military intervention, would never be recognized by the United States and the international community," it said. "He emphasized 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."

- CNN