Russia executed a de facto military takeover of a strategic region in Ukraine as the parliament in Moscow gave President Vladimir Putin a green light Saturday to proceed to protect Russian interests. The newly installed government in Kiev was powerless to react to the swift takeover of Crimea by Russian troops already in Ukraine and more flown in, aided by pro-Russian Ukrainian groups.
Ukraine's interim president put the country's military on combat alert, while the country's prime minister said a Russian military intervention would lead to war and the country's foreign minister asked foreign powers to help protect the country's territory.
In the wake of the vote Putin and President Barack Obama held a 90-minute call. The Kremlin said that Russia reserved the right to protect its interests and those of Russian speakers in the case of violence in Crimea and eastern Ukraine. The White House said Obama expressed the sense that Russia's actions were a "clear violation" of Ukrainian sovereignty.
"The United States will suspend upcoming participation in preparatory meetings for the G-8. Going forward, Russia's continued violation of international law will lead to greater political and economic isolation," the White House said.
Ukraine's ambassador to the United Nations told an open meeting of the UN Security Council that Russia had "brutally violated" the UN charter. Russia's UN ambassador, Vitaly Churkin, rejected those claims. The U.S. ambassador, meanwhile, said it was time for Russia's intervention to end.
"The Russian military must stand down," Samantha Power said after Churkin's statement.
European Union foreign ministers set an emergency meeting for Monday in Brussels to discuss the situation. NATO Secretary General Anders Fogh Rasmussen called on Russia to respect Ukraine's sovereignty and set a meeting of the organization's ambassadors for Sunday.
Defense Secretary Chuck Hagel spoke with Russia's defense minister, Sergei Shoigu, a conversation that a senior defense official told NBC News was "tense."
The unanimous vote in an emergency session formalized what Ukrainian officials described as an invasion of Russian troops in the strategic region of Crimea. With pro-Russian protests breaking out in other parts of Ukraine, Moscow now could send its military elsewhere in Ukraine.
"I'm submitting a request for using the armed forces of the Russian Federation on the territory of Ukraine pending the normalization of the socio-political situation in that country," Putin said before the vote.
(Read more: Russia likely to get what it wants in showdown)
Putin's call came as pro-Russian demonstrations broke out in Ukraine's Russian-speaking east, where protesters raised Russian flags and beat up supporters of the new Ukrainian government.
Russia's move sharply raised the stakes in the conflict following the ouster of Ukraine's pro-Russian president last week by a protest movement aimed at turning Ukraine toward the European Union and away from Russia.
Ukraine has accused Russia of a "military invasion and occupation" -- a claim that brought an alarming new dimension to the crisis, and raised fears that Moscow is moving to intervene on the strategic peninsula where Russia's Black Sea fleet is based.
"Look who is in power now in Ukraine---radicals, nationalists, fascists," one Russian legislator said during the course of parliament's debate.
President Obama warned Moscow on Friday "there will be costs" if Russia intervenes militarily. In Saturday's parliamentary session in Moscow, one Russian legislator said Obama had crossed a "red line" and the upper house recommended the Russian ambassador in Washington be recalled. It will be up to Putin to decide whether that happens.
In Crimea, the pro-Russian prime minister who took office after gunmen seized the regional Parliament claimed control of the military and police there and asked Putin for help in keeping peace, sharpening the discord between the two neighboring Slavic countries.
Ukraine's acting president, Oleksandr Turchynov, said the election of Sergei Aksyonov as prime minister of Crimea was invalid.
It was the latest escalation following the ouster of Ukraine's pro-Russian president last week by a protest movement aimed at turning Ukraine toward the European Union and away from Russia.
Ukraine's population is divided in loyalties between Russia and Europe, with much of western Ukraine advocating closer ties with the European Union while eastern and southern regions look to Russia for support. Crimea, a semi-autonomous region of Ukraine, is mainly Russian-speaking.
Ukrainian Prime Minister Arseny Yatsenyuk opened a Cabinet meeting in the capital, Kiev, by calling on Russia not to provoke discord in Crimea.
"We call on the government and authorities of Russia to recall their forces, and to return them to their stations," Yatsenyuk was quoted as saying by the Interfax news agency. "Russian partners, stop provoking civil and military resistance in Ukraine."
(For more from NBC News on the Ukraine crisis, click here)
—By The Associated Press. Reuters and CNBC.com contributed to this report.