Russian President Vladimir Putin and 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 declared "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 port city of Sevastopol, where Russia's Black Sea fleet is based.
The Kremlin said on its website that Crimea "shall be deemed accepted in the Russian Federation from the date of signing the treaty."
The treaty was signed shortly after Mr. Putin told Russia's parliament in a televised address that Crimea has always been an "inalienable" part of Russia, and a day after he signed a decree recognizing the peninsula as "a sovereign and independent country.
But President Putin said Tuesday that the referendum complied with democratic and international norms.
U.S. Vice President Joe Biden is in Poland Tuesday for talks with regional allies concerned about Russia's military incursion into Crimea. Biden is meeting with the leaders of Poland and the Baltic states of Estonia, Lithuania and Latvia.
After many warnings, Washington and Brussels imposed their first sanctions on Russian officials Monday for their backing of the Crimean vote.
Crimean officials said the final ballot count showed 97 percent of voters favoring independence from Ukraine.
But senior White House officials told reporters they have "concrete evidence" that some ballots in the referendum were pre-marked when they arrived in cities before the vote.
The Obama administration, the European Union and a host of legal analysts have repeatedly said the Crimean referendum violates the Ukrainian constitution and international law.
U.S. President Barack Obama Monday declared a freeze on the assets of seven Russian officials and four Ukrainians who have supported Crimea's separation from Ukraine. He pledged "unwavering" support for Ukraine and said more sanctions on Russia are possible.
"We'll continue to make clear to Russia that further provocations will achieve nothing except to further isolate Russia and diminish its place in the world. 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."
A White House official told reporters the Russian officials targeted for sanctions are "cronies" of President Putin. Mr. Putin himself was not the subject of any punitive measures.
Mr. Obama said Vice President Biden is discussing the situation with NATO leaders in Europe. The president himself is slated to to go Europe next week.
Monday, the European Union designated 21 officials from Russia and Ukraine for travel bans and trade sanctions.
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.
In Kyiv Sunday, Ukraine's interim Prime Minister Arseniy Yatsenyuk called the Moscow-backed Crimea vote "a circus spectacle" directed at gunpoint by Russia.