Russian President Vladimir Putin and officials from Crimea signed a treaty Tuesday to make the Black Sea peninsula part of Russia, just two days after it voted to secede from Ukraine in a referendum the United States and the European Union call "illegal."
Mr. Putin signed the document with the prime minister of Crimea's regional government, the speaker of Crimea's parliament, and the mayor of the Crimean city of Sevastopol, where Russia's Black Sea fleet is based.
Hours later, Russian and Ukrainian news media quoted a Ukrainian military spokesman as saying that Russian forces had attacked Ukrainian troops at a base in Crimea's main city, Simferopol, killing one serviceman.
Earlier Tuesday, Mr. Putin said told Parliament that Crimea has always been an "inalienable" part of Russia.
He said Sunday's referendum complied with democratic and international norms.
In his speech, the president insisted Russia has always respected Ukraine's territorial integrity and neither wants nor needs to "partition" Ukraine.
But he criticized Soviet leader Nikita Khrushchev's decision to transfer Crimea from Russia to Ukraine in 1954, when both countries were constituent republics of the Soviet Union. When Crimea ended up as part of independent Ukraine after the fall of the Soviet Union in 1991, he said, Russia felt not simply "robbed," but "plundered."
Mr. Putin also said that after the Russian Revolution of 1917, "significant historical territory" of southern Russia, including "present-day southeastern Ukraine," was included in the Ukrainian republic of the Soviet Union "without regard to the ethnic composition of the population."
Mr. Putin described last month's ouster of Ukraine's pro-Russian president, Viktor Yanukovych, as a coup carried out mainly by "nationalists, neo-Nazis, Russophobes and anti-Semites".
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.
On Tuesday, U.S. Vice President Joe Biden is in Poland to meet with Prime Minister Donald Tusk. Biden called Russia's move a "land grab" and said Washington is committed to defending the security of its NATO allies on Russian borders. Biden later meets with the leaders of the Baltic states Estonia, Latvia, and Lithuania.
Also in response to Russia's moves, Britain suspended military cooperation with Russia in light of the dispute over Crimea.
The move cancels a planned naval exercise and suspends a British Royal Navy ship visit to Russia.
Crimean officials say the final ballot count showed 97 percent of voters favoring independence from Ukraine.
But senior White House officials say they have "concrete evidence" that some ballots in the referendum were pre-marked before the vote.
The Obama administration, the European Union and a host of legal analysts say the Crimean referendum violates the Ukrainian constitution and international law. The U.S. and E.U. have imposed economic and travel sanctions on senior Russian and Ukrainian officials who have supported Crimea's separation from Ukraine.
"The international community will continue to stand together to oppose any violations of Ukrainian sovereignty and territorial integrity, and continued Russian intervention in Ukraine will only deepen Russia's diplomatic isolation and exact a greater toll on the Russian economy."
In New York, United Nations Secretary-General Ban Ki-moon on Monday voiced "deep disappointment" with Sunday's secession vote in Crimea. A spokesman said Mr. Ban, who has sought to resolve the crisis, fears the vote will further heighten tensions between Kyiv and Moscow.