Crimea's parliament declared the region an independent state and applied to become part of Russia on Monday, a day after a referendum in the southern Ukrainian region showed overwhelming support for joining the Russian Federation.
The parliament "made a proposal to the Russian Federation to admit the Republic of Crimea as a new subject with the status of a republic," according to a statement on its website.
A Crimean parliamentary delegation was expected to arrive in Moscow on Monday to discuss the procedures required for the Black Sea peninsula to become part of the Russian Federation.
In response to the Crimea vote, European Union foreign ministers have agreed to impose sanctions including travel bans and asset freezes on 21 officials from Russia and Ukraine, Lithuania's foreign minister said on Monday.
After a meeting lasting around three hours, the EU's 28 foreign ministers quickly reached agreement on the list of those to be sanctioned for their part in Russia's seizure of Crimea and Sunday's referendum to secede from Ukraine and join Russia.
"(Foreign Affairs Council) just agreed on sanctions - travel restrictions & assets freeze against 21 officials from Ukraine & Russia," Linan Linkevicius wrote in a message on Twitter.
He added that more measures would follow in a few days, when EU leaders meet for a summit in Brussels. They are expected to expand the list to include more senior figures closer to Russian President Vladimir Putin.
Earlier Monday, Russia's foreign ministry has called on Ukraine to become a federal state and call fresh elections.
In a statement, the ministry urged Ukraine's parliament to call a constitutional assembly which could draft a new constitution to make the country federal, handing more power to its regions.
The foreign ministry said the proposals are part of its efforts to ease the tensions in Ukraine by diplomatic means.
Moscow insisted that Ukrainian regions should get broader autonomy and that the country should adopt a "neutral political and military status."
Ukraine's parliament, seeking to boost the country's military force in the face of Russia's takeover of the Crimea peninsula, endorsed on Monday a presidential decree to carry out a partial mobilization involving 40,000 reservists.
Andriy Parubiy, Secretary of the National Security and Defense Council, told parliament that 20,000 reservists would be deployed within the armed forces and the rest would be used within the newly-created National Guard.
British Foreign Secretary William Hague said Monday that he is confident that the European Union will ratchet up pressure on Russia over its role in the breakaway of Ukraine's Crimea region by imposing sanctions on people linked to the secession of the peninsula.
The 28-nation EU condemned the Crimea referendum which overwhelmingly backed a return to Russia, and the EU foreign ministers were assessing on Monday who to target for asset freezes and travel bans.
Hague said that he was confident that an agreement could be reached on the list of officials to hit with sanctions and hinted that more measures against Russia could be taken at a summit of EU leaders starting Thursday.
As state media in Russia carried a startling reminder of its power to turn the United States to "radioactive ash," U.S. President Barack Obama spoke to Vladimir Putin, telling the Russian president that he and his European allies were ready to impose "additional costs" on Moscow for violating Ukraine's territory.
The Kremlin and the White House issued statements saying Obama and Putin saw diplomatic options to resolve the gravest crisis in East-West relations since the Cold War.
But Obama said Russian forces must first end "incursions" into its ex-Soviet neighbor while Putin renewed his accusation that the new leadership in Kiev, brought to power by an uprising last month against his elected Ukrainian ally, were failing to protect Russian-speakers from violent Ukrainian nationalists.
Moscow defended a military takeover of the majority ethnic Russian Crimea by citing a right to protect "peaceful citizens." Ukraine's interim government has mobilized troops to defend against an invasion of its eastern mainland, where pro-Russian protesters have been involved in deadly clashes in recent days.
Head of the referendum election commission Mikhail Malyshev told a televised news conference that final tally from Sunday's vote was 96.8 percent in favor of splitting from Ukraine. He also said that the commission has not registered a single complaint about the vote.
The referendum was widely condemned by Western leaders who were planning to discuss economic sanctions to punish Russia on Monday.
Turnout was 83 percent, he added - a high figure given that many who opposed the move had said they would boycott the vote.
Ukraine's new government in Kiev called the referendum a "circus" directed at gunpoint by Moscow.
The Crimean peninsula has been seized for two weeks now by troops under apparent Russian command.
Russia's lower house of parliament will pass legislation allowing Crimea to join Russia "in the very near future," news agency Interfax cited its deputy speaker as saying on Monday.
"Results of the referendum in Crimea clearly showed that residents of Crimea see their future only as part of Russia," Sergei Neverov was quoted as saying.
U.S. and European officials say military action is unlikely over Crimea, which Soviet rulers handed to Ukraine 60 years ago. But the risk of a wider Russian incursion, as Putin probes Western weakness and tries to restore Moscow's influence over its old Soviet empire, leaves NATO calculating how to help Kiev without triggering what some Ukrainians call "World War Three."
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