Russian President Vladimir Putin and Crimean leaders have signed a treaty to make Crimea part of Russia, angering the United States and European Union.
Mr. Putin told the Russian parliament that Crimea has always been an "inalienable" part of Russia. He said Sunday's referendum, in which Crimean voters decided to break away from Ukraine and join Russia, was legal.
Mr. Putin criticized Soviet leader Nikita Khrushchev for placing Crimea under Ukrainian control in 1954. When Crimea ended up as part of independent Ukraine in 1991, Mr. Putin said Russia had been "plundered."
He said last month's ouster of Ukraine's pro-Russian president, Viktor Yanukovych, was a coup by "nationalists, neo-Nazis, and anti-Semites."
U.S. Secretary of State John Kerry told a group of university students in Washington that he was surprised and disappointed by what he called Mr. Putin's interpretation of the facts.
Kerry said Russia is on the wrong side of history. He said when a region secedes from a country, it does it under the constitution -- not at the butt of a gun.
Crimean officials say the final ballot count from Sunday's referendum shows 97 percent of voters favored independence from Ukraine.
Senior White House officials say they have "concrete evidence" that some ballots were marked before the vote.
Ukrainian Prime Minister Arseniy Yatsenyuk said Tuesday that his country's law enforcement agencies have "convincing evidence" Russia's special services are involved in unrest in eastern Ukraine.
Separately, Mr. Yatsenyuk told CNN there is "a strong possibility" of a Russian invasion of Ukraine.