The authorization cited a threat to the lives of Russian citizens and soldiers stationed in Crimea and other parts of Ukraine, and provided a blunt answer to President Obama, who on Friday pointedly warned Russia to respect Ukraine’s territorial sovereignty.

Even before Mr. Putin’s statement in Moscow, scores of heavily armed soldiers had tightened their grip on the Crimean capital, Simferopol, surrounding government buildings, shuttering the airport, and blocking streets, where they deployed early Friday.

Large pro-Russia crowds rallied in the eastern Ukrainian cities of Donestk and Kharkiv, where there were reports of violence. In Kiev, the Ukrainian capital, fears grew within the new provisional government that separatist upheaval would fracture the country just days after civil unrest ended in the ouster of President Viktor F. Yanuovych, a Kremlin ally who fled to Russia.

n Crimea, in the south, scores of heavily armed men fanned out across the center of the regional capital, Simferopol. They wore green camouflage uniforms with no identifying insignia, but they spoke Russian and were clearly part of a Russian military mobilization. In Balaklava, a long column of military vehicles blocking the road to a border post bore Russian plates.

The Russian mobilization was cited by American military and intelligence analysts as the basis for Mr. Obama’s warning that “there will be costs” if Russia violated Ukrainian sovereignty.

On Saturday morning, there was no immediate response from the White House; officials had acknowledged on Friday that Washington’s options were limited.

There was also limited response from Europe. Carl Bildt, the Swedish foreign minister, issued a statement saying that Russia’s actions in Crimea were “contrary to international law and the principles of European security.”

Mr. Yanukovych’s refusal, under Russian pressure, to sign new political and free trade agreements with the European Union last fall set off the civil unrest that last month led to the deaths of more than 80 people, and ultimately unraveled his presidency.

While Western leaders grappled for a response on Saturday, a Ukrainian military official in Crimea said Ukrainian soldiers had been told to “open fire” if they came under attack by Russia troops or others.

In addition to the risk of open war, it was a day of frayed nerves and set-piece political appeals that recalled ethnic conflicts of past decades in the former Soviet bloc, from the Balkans to the Caucasus.

On Saturday morning, the pro-Russia prime minister of Crimea, Sergei Aksyonov, declared that he had sole control over the military and the police in the disputed peninsula and appealed to Mr. Putin for Russian help in safeguarding the region. He also said a public referendum on independence would be held on March 30.

The Kremlin has denied any attempt to seize Crimea, where it maintains important military installations, including the headquarters of its Black Sea Fleet. But the Kremlin quickly issued a statement saying that Mr. Aksyonov’s plea “would not be ignored” and within hours the Federation Council, the upper chamber of Parliament, had authorized military action.

The authorization, while citing Crimea, covered the use of Russian forces in the entire “territory of Ukraine” and its time frame extended indefinitely “until the normalization of the sociopolitical environment in the country.” Parliament also asked Mr. Putin to withdraw Russia’s ambassador to the United States.

Officials in the Ukrainian capital, Kiev, reacted angrily and reiterated their demands that Russia pull back its forces, and confine them to the military installations in Crimea that Russia has long leased from Ukraine.

“The presence of Russian troops in Crimea now is unacceptable,” said acting Prime Minister Arseniy P. Yatsenyuk. Decrying the Russian deployment as a “provocation,” he added, “We call on the government of the Russian Federation to immediately withdraw its troops, return to the place of deployment and stop provoking civil and military confrontation in Ukraine.”

For the new government, the tensions in Crimea created an even more dire and immediate emergency than the looming financial disaster that they had intended to focus on in their first days in office.

A $15 billion bailout that Mr. Yanukovych secured from Russia has been suspended as a result of the political upheaval and Ukraine is in desperate need of an assistance package. Mr. Yatsenyuk had said that the government’s first responsibility was to begin negotiations with the International Monetary Fund and start to put in place the economic reforms and painful austerity measures that the fund has requested in exchange for help.

In Crimea, however, officials said they did not recognize the new government, and declared that they had taken control.

Mr. Aksyonov, the regional prime minister, said he was ordering the regional armed forces, the Interior Ministry troops, the Security Service, border guards and other ministries under his direct control.

He added, “I ask anyone who disagrees to leave the service.”

As soldiers mobilized across the peninsula, the region’s two main airports were closed, with civilian flights canceled, and they were guarded by heavily armed man in military uniforms.

Similar forces surrounded the regional Parliament building and the rest of the government complex in downtown Simferopol, as well as numerous other strategic locations, including communication hubs and a main bus station.

Adding to the strange tableau, a crowd of about 400 people gathered near the Parliament building in Simferopol to denounce the United States.

Some waved orange and black flags, while others held placards that said “Free Ukraine from US Occupation” and “The USA works with Fascism.”

One elderly woman held up a photo of President Obama with a red line through it and the caption “Yankee Go Home.” She then helped lead part of the crowd in a chant of “Yankees Go Home.”

Near the entrance Balaklava, the site of a Ukrainian customs and border post near Sevastopol, the column of military vehicles with Russian plates included 10 troop trucks, with 30 soldiers in each, two military ambulances and five armored vehicles. The column was not moving.

oldiers, wearing masks and carrying automatic rifles, stood on the road keeping people away from the convoy, while some local residents gathered in a nearby square waving Russian flags and shouting, “Russia! Russia!”

Hardly all of the sentiment in Crimea was pro-Russian. At a checkpoint on the main road from Simferopol to Sevastopol, someone had hung a big banner with red lettering. “Russia has always been the graveyard of evil ideas,” it said. “You cannot win over a graveyard, you can only stay in it forever.”

As with the troops in downtown Simferopol, the soldiers did not have markings on their uniforms. They would not say where they were from.

There were also other unconfirmed reports of additional Russian military forces arriving in Crimea, including Russian ships landing in Fedosiya, in eastern Crimea.

On Friday, American officials said that they had confirmed reports of Russian troop deployments in Crimea including special forces and specially trained marine and airborne units. Ilyushin transport planes were said to have ferried in troops and there were reports of Russian helicopter flights.

Crimea, while part of Ukraine, has enjoyed a large degree of autonomy under an agreement with the federal government in Kiev since shortly after Ukrainian independence from the Soviet Union.

The strategically important peninsula, which has been the subject of military disputes for centuries, has strong historic, linguistic and cultural ties to Russia. The population of roughly two million is predominantly Russian, followed by a large number of Ukrainians, and Crimean Tatars, people of Turkic-Muslim origin.

Meanwhile, outpourings of pro-Russia sentiment were also underway in eastern Ukraine.

In Kharkiv, pro-Russian demonstrators rallied and then seized control of a government building, pulled down the blue-and-yellow Ukrainian flag and raised the blue, white and red Russian one. Scores of people were injured as protesters scuffled with supporters of the new government in Kiev.

In Donetsk, a crowd of several thousand people held a rally in the city-center, local news agencies reported, with many chanting pro-Russian slogans and demanding a public referendum on secession from Ukraine.

There were also signs on Saturday of concern among Ukrainian business leaders over an effort by several European countries, including Austria and Switzerland, to freeze Mr. Yanukovych’s assets as well as those of his family members and other prominent associates.