With Kiev's new government weak and in disarray, Russia has made an aggressive move into Crimea following a unanimous vote by Russia's upper house of parliament Saturday, which gave President Vladimir Putin a green light to send troops to Ukraine without specifying where.
Ukrainian Prime Minister Arseniy Yatsenyuk is warning Russia that a continued military intervention will mean war between the neighboring countries; acting Ukrainian President Oleksandr Turchynov said he put the country's armed forces on combat alert following Saturday's vote, during which Russian legislators also asked Putin to withdraw Moscow's ambassador to Washington.
Russian legislators said they were insulted by U.S. President Barack Obama's statement on Ukraine Friday, in which Obama said the U.S. is "deeply concerned by reports of military movements taken by the Russian Federation inside of Ukraine."
Obama went on to say there would be "costs for any military intervention in Ukraine."
The White House says Obama held a 90 minute phone conversation with Putin Saturday, in which he expressed deep concern for what the United States calls a clear violation of Ukrainian sovereignty and international law.
Obama administration officials also say the United States is suspending participation in meetings to prepare for the G8 economic summit later this year in Sochi, Russia, which recently hosted the Winter Olympic Games.
According to Russian news agencies, Putin told the U.S. president that Moscow reserves the right to protect Russian speakers if there is violence in Crimea or eastern Ukraine.
On Saturday, Ukraine's deposed president, Viktor Yanukovych, and Sergei Aksenov, Crimea's new prime minister, appealed for Russian troops to enter Ukraine's Autonomous Republic of Crimea.
Aksenov's Russia Unity Party won only three parliament seats in regional elections in 2010, and won no seats in Ukraine's 2012 national elections.
Story continues after video: Elizabeth Arrott, on the ground in Simferopol.
On Thursday, armed Russian-speaking men invaded Crimea's parliament. At gunpoint, a slim majority elected Aksenov.
UN calls for 'cool heads'
Saturday's vote by Russia’s parliament triggered an emergency session of the U.N. Security Council, during which Yuriy Sergeyev, Ukrainian Ambassador to the United Nations, said15,000 Russian troops are already in Crimea and that their numbers are “increasing every hour.” Sergeyev said his country has called upon the world deliberative body to do everything possible to stop what he called the aggression.
He told reporters after the meeting that Kiev is willing to work with Moscow about its concerns, but must pull back its troops.
“We are ready for consultations, but what we demand is all the troops to be withdrawn; immediately withdrawn, because they are illegally present there," he said.
Russia earlier rejected bilateral talks with Ukraine’s new government. Russian Ambassador Vitaly Churkin said Western governments were trying to “whip up” the situation in Ukraine over preceding months, encouraging protesters who were angry about the previous government’s decision not to sign an association agreement with the European Union.
On Russian troops, Churkin told the council that President Putin had asked parliament for the possibility of the use of force in Ukraine, but that Putin has not yet acted on its approval.
Moscow has not confirmed new troop deployments, saying only that current movements are in conformity with existing bilateral agreements to protect its naval base at Sevastopol in Crimea.
U.N. Secretary-General Ban Ki-moon said in taped remarks after speaking with Putin by phone Saturday that “cool heads must prevail and dialogue must be the only tool in ending this crisis," while Security Council members officially called for de-escalation of tensions and international mediation to end the crisis.
NATO announced Saturday that its ambassadors will meet Sunday in Brussels to discuss the escalating crisis. A meeting of the NATO-Ukraine Commission is scheduled as well.
In Moscow, political analyst Pavel Felgenhauer says Moscow is following a political strategy that worked well in the Soviet era.
"This is from the Russian textbook — there is nothing new at all," he said, referring to Soviet-era invasions. "It happened in Afghanistan. It happened in Hungary."
In those cases, Soviet troops invaded countries after appeals by leaders installed by the Kremlin.
In Crimea, Moscow acted before the nicety of an appeal by the region's new prime minister — and during a period with high political tension, but little violence.
Starting Friday, Russian army troops took over Crimea's three airports, and military helicopters and transport planes shuttled troops and supplies into the peninsula. Russian soldiers and Navy ships blockaded Ukrainian military bases. Armed checkpoints manned by Russian-speaking men now control the sole highway from the mainland to the peninsula. Russian consular officials started distributing Russian passports to policemen in Crimea.
"Russia has started blatant aggression against Ukraine under the guise of military exercises," said Ukraine's interim President Oleksandr Turchynov. "The Russian Federation has sent troops to Crimea, which have not only seized the Crimean parliament and the Council of Ministers but are also trying to take control of communication facilities and the bases where the servicemen are stationed."
Only two months ago, Russian state television praised Ukrainians as their Slavic brothers. In a total switch, state television now describes Ukraine as a country controlled by "fascist nationalists." Television screens show videos of Russian army tanks churning through mud, part of a 150,000-man military exercise across the border from eastern Ukraine.
Dmitri Trenin, director of the Carnegie Moscow Center, says the military exercise is designed to tell Kiev and the West to back off from Russian-speaking areas of Ukraine.
"The timing of this is clearly sending a message to the people in Kiev — don't go too far, don't try to establish 'constitutional order' in Crimea, don't intervene by force in Eastern Ukraine," he said in a conference call. "It's also, I think, a message to Washington and NATO, in the sense that Russia is prepared to defend its interests in this part of the world."
Emboldened by Russia's show of force, armed men on Saturday seized government buildings in Eastern Ukraine's two largest cities
— Kharkiv and Donetsk. Soon, Russian flags flapped from the rooftops.
WATCH: Pro-Russian demonstrators storm the Kharkiv administration (courtesy: rferl.org).
Some regional analysts warn that Russia may be biting off more than it can chew.
"Right now our peacekeeping units are going to be tied down in Crimea, and we don't have that many peacekeeping units," said Felgenhauer who specializes in military analysis.
And it is unclear how deep the support is in Crimea for Russian annexation. The prime minister says he will hold a referendum on Crimea's status on March 30.
The majority of Crimea's 2 million people are native Russian speakers, but Kiev has ruled Crimea for nearly 70 years. A large portion of inhabitants identify themselves as Russian speaking Ukrainians.
In addition, Muslim Tatars make up 15 percent of Crimea's population. During the first half of the 20th century Kremlin policies killed about half the population — through famine in the 1920s and 1930s and mass deportation in 1944. As a result, Crimean Tatars strongly oppose rule by Moscow.
If Russia's occupation turns violent, Turkey could step in to defend the Tatars. The simplest way would to be close the Bosphorus strait, the exit route for about one third of Russia's oil exports.
Felgenhauer said of the Turkish government: "They could get rather nasty with Russia. They could put serious pressure on the Russian government."
Ukraine's central government has its own levers. It could cut off a water pipe from the continent that is a primary source of drinking water to Crimea's arid north. Tourism, the economic mainstay for much of Crimea's population, could plummet if political tensions over sovereignty remain high.
And Russia can expect sanctions from the West, its major trading partner.
For starters, Western leaders would probably boycott the June summit of G8 countries. President Putin is planning to host the summit in Sochi, which lies only 400 kilometers across the Black Sea from Crimea.
Few options for US
Some U.S. experts agree that Obama's options in the Ukraine crisis are limited
, and that he is not seriously considering use of military force, although he is said to have talked with advisers about the idea of moving warships to the region.
Ukraine is not a member of NATO, and the Western alliance is not required to come to its defense.
Economic options appear more likely.
One possibility is for the U.S. to impose sanctions on Russia's financial institutions.
Tim Brown, senior fellow at globalsecurity.org, says another is to freeze Russian leaders' offshore bank accounts.
"It's almost certain that Putin has a large, or several large, bank accounts of his own, and I would imagine that those are going to get frozen," Brown said. "So when they say there are going to be costs, it's not going to be to the Russian people. It's more along the lines it's going to be the Russian leadership personally."
While Saturday's White House statement said the president told Putin the U.S. would suspend its participation in preparatory meetings for the Group of Eight (G8) summit, Obama and his aides are reported to have discussed canceling his trip to the summit altogether, or even kicking Russia out of the G8.
Scrapping a possible trade agreement with Moscow may be another alternative.
U.S. leverage is diminished by the need for Russia's help in negotiating a nuclear deal with Iran and working to end Syria's war. Also, the U.S. uses Russian supply routes to move troops and equipment out of Afghanistan.
So far, the possible costs have not been enough to discourage Putin from sending Russian troops to Ukraine.
Ukraine's fugitive president Viktor Yanukovych speaks at a news conference in Rostov-on-Don, a city in southern Russia, Feb. 28, 2014.
On Friday, ousted Urkrainian President Yanukovych resurfaced in the southern Russian city of Rostov-on-Don where he held a news conference, calling on his opponents to stop what he called the "horrible lawlessness" in Ukraine.
Ukrainians had mixed reactions to this first public appearance of Yanukovych who fled Kiev last week.
While Kiv and western Ukraine have risen up against Yanukovych, he remains popular in the Russian-speaking eastern and southern regions where economic and cultural ties with Russia remain strong.
His remarks were broadcast around the country on giant television screens.
Galina Shurko, resident of the western Ukraine city of Lviv, is not a supporter of the ousted leader.
"You know, we are really surprised that he's still saying something," said Shurko. "We don't even like to listen to him because of all this pain in our hearts and everything that he has done to Ukraine."
Meanwhile, Karina, a resident of the northeastern city of Kharkiv, said Yanukovych's re-surfacing in Russia was the logical thing to do.
"Sorry, but what is Viktor Yanukovych to do when some strange people came to power and simply act as some junkies? What should he do? Where should he go? He could have been killed, as simple as that, of course he went to Rostov-on-Don," she said.
Lena Kleshevnykova, another resident of Kharkiv — Ukraine's second largest city — is a staunch supporter of the Yanukovych.
"I still consider him our president because the new government came to power in an unlawful way, with military aggression," said Kleshevnykova.
Some information for this report was provided by VOA correspondent Elizabeth Arrott reporting from Simferopol, VOA correspondent Kent Klein reporting from Washngton, and VOA correspondent Margaret Besheer reporint from the United Nations.