BRUSSELS, March 17 - The United States and the European Union imposed personal sanctions on Monday on Russian and Crimean officials involved in the seizure of Crimea from Ukraine as Russian President Vladimir Putin signed a decree recognizing the region as a sovereign state.

The moves heightened the most serious East-West crisis since the end of the Cold War, following a disputed referendum in the Black Sea peninsula on Sunday in which Crimea's leaders declared a Soviet-style, 97-percent vote to secede from Ukraine.

Within hours, the Crimean parliament formally asked that Russia "admit the Republic of Crimea as a new subject with the status of a republic.” Putin will on Tuesday address a special joint session of Russia's State Duma, or parliament, which could take a decision on annexation of the majority ethnic-Russian region.

That would dismember Ukraine, a former Soviet republic once under Moscow's thumb, against its will. Kiev and the West said the referendum, held under armed Russian occupation, violated Ukraine's constitution and international law.

Russian forces took control of Crimea in late February following the toppling of Ukrainian President Viktor Yanukovych after deadly clashes between riot police and protesters trying to overturn his decision to spurn a trade and cooperation deal with the EU in favor of cultivating closer ties with Russia.

U.S. President Barack Obama slapped sanctions on 11 Russians and Ukrainians blamed for the seizure, including Yanukovych, and Vladislav Surkov and Sergei Glazyev, two aides to Putin.

Putin himself, suspected in the West of trying to resurrect as much as possible of the former Soviet Union under Russian leadership, was not on the blacklist. A White House spokesman declined to rule out adding him at a later stage.

Amid fears that Russia may move into eastern Ukraine where there is a significant Russian-speaking community, Obama warned that "further provocations" would only increase Moscow's isolation and exact a greater toll on its economy.

"If Russia continues to interfere in Ukraine, we stand ready to impose further sanctions," he said.

A senior U.S. official said Obama's order cleared the way to impose sanctions on people associated with the arms industry and targets "the personal wealth of cronies" of the Russian leadership.

In Brussels, the EU's 28 foreign ministers agreed to subject 21 Russian and Ukrainian officials to visa restrictions and asset freezes for their roles in the events. They included three Russian military commanders in Crimea and districts bordering on Ukraine.

There were only three names in common on the U.S. and European lists - Crimean Prime Minister Sergey Aksyonov, Crimean parliament Speaker Vladimir Konstantinov and Leonid Slutski, chairman of the Russian Duma's committee on the Russian-led Commonwealth of Independent States, or CIS, grouping former Soviet republics. The EU blacklisted Yanukovich earlier this month.

The U.S. list appeared to target higher-profile Russian officials close to Putin, including a deputy Russian prime minister, while the EU went for mid-ranking officials who may have been more directly involved on the ground.

Washington and Brussels said further steps could follow in the coming days if Russia does not back down and formally annexes Crimea.

Obama said he would travel to Europe next week and that Vice President Joe Biden was headed on Monday to Poland and Lithuania to reassure U.S. allies in the region.

A senior Obama administration official said there was "concrete evidence" that some ballots in the Crimea referendum arrived in some Crimean cities pre-marked.

A complete preliminary count of Sunday's vote showed that 96.77 percent of voters opted to join Russia, the chairman of the regional government commission overseeing the referendum, Mikhail Malyshev, announced on television.

Officials said the turnout was 83 percent. Crimea is home to 2 million people. Members of the ethnic Ukrainian and Muslim Tatar minorities had said they would boycott the poll, held just weeks after Russian forces took control of the peninsula. (rt/ez)