The Ukrainian army are on “high alert” in Crimea after Russia allegedly moved 6,000 troops into the border region, taking control of airports and roads.
Ukraine’s Defence Minister, Ihor Tenyukh, gave the first estimate of numbers following silence from Russia over reports they were deploying troops in the area but did not give any further details.
The Russian parliament granted Vladimir Putin's request for permission to use the country's military in Ukraine on Saturday afternoon.
"In connection with the extraordinary situation in Ukraine, the threat to the lives of citizens of the Russian Federation, our compatriots, and the personnel of the armed forces of the Russian Federation on Ukrainian territory [in Crimea] ... I submit a proposal on using the armed forces of the Russian Federation on the territory of Ukraine until the normalisation of the socio-political situation in the country," the statement said.
Earlier in the day, Russia's lower house of parliament asked Mr Putin to "take measures to stabilise the situation in Crimea and use all available means to protect the people of Crimea from tyranny and violence".
Crimean politician Sergei Aksyonov had earlier claimed he was in control of the area and declared that the armed forces, police, national security service and border guards will answer only to his orders.
Mr Aksyonov, who is head of the main pro-Russian party on the peninsula, appealed to Russia "for assistance in guaranteeing peace and calmness on the territory of the autonomous republic of Crimea".
He was voted in by the Crimean parliament on Thursday after pro-Russia gunmen seized the building and as tensions soared over the region's resistance to the new authorities in Kiev following the removal of Viktor Yanukovych.
Border guard ships have reportedly left bases to prevent the capture of military bases and ships in the Crimea region.
The move comes after pro-Russian authorities in Crimea and Russia's Black Sea fleet agreed to gThe Ukrainian army are on “high alert” in Crimea after Russia allegedly moved 6,000 troops into the border region, taking control of airports and roads.uard buildings in the region together, according to Russia's RIA news agency.
The international airport at Simferopol, the main city, confirmed its airspace was closed on Saturday after armed men took control on Friday.
"Due to limitations in the use of the airspace, the airport has temporarily suspended receiving flights," the airport said in a written statement.
Ukrainian military sources say that Russian servicemen also control military airfields in Belbek, near Sevastopol, and in Kirovskoye in eastern Crimea.
The Prime Minister of Ukraine vowed that his country will not be drawn into war by Russian “provocations”.
Speaking on Saturday morning, Arseny Yatseniuk appealed to Mr Putin’s government to halt military movements in the border region.
“It is unacceptable when armoured Russian military vehicles are out in the centre of Ukrainian towns,” he said before a government meeting in Kiev.
Russia, which has a naval base in Crimea, insisted any movements by its military in Crimea are in line with agreements with Ukraine over its naval fleet.
In pictures: Crisis in Ukraine
In pictures: Crisis in Ukraine
1/11 Demonstrations in Crimea
Crimean Tatars drag away a police officer in front of a local government building in Simferopol
2/11 Demonstrations in Crimea
Pro-Russian activists pray outside the Crimean Parliament building in Simferopol
3/11 Demonstrations in Crimea
Crimean Tatars hold flags during rallies near the Crimean parliament building in Simferopol
4/11 Demonstrations in Kiev
Young girls chant the song 'Glory to Ukraine' at Independence Square in central Kiev
5/11 Demonstrations in Crimea
A man receives medical treatment after he was injured in clashes during rallies near the Crimean parliament building
6/11 Demonstrations in Crimea
Pro-Ukrainian activists hold placards reading "Crimea +Ukraine is love" during a rally in front of the Crimean parliament in Semfiropol
7/11 Demonstrations in Kiev
Protestors capture a military armoured vehicle in central Kiev
8/11 Demonstrations in Kiev
An old man stands with an Ukrainian flag on Kiev's Independence Square
9/11 Demonstrations in Kiev
A man lays flowers at one of the barricades heading to Kiev's Independence Square
10/11 Demonstrations in Kiev
Flowers cover the ground and barricades where protesters were killed in a recent clash with riot police in Kiev's Independence Square
11/11 Demonstrations in Kiev
A self-defense unit patrolling the city centre in Kiev, Ukraine
The Russian foreign ministry accused Kiev politicians of trying to destabilise the situation on the peninsula.
"In Russia, we are extremely concerned about the recent developments in Crimea," a statement said.
"We believe it is extremely irresponsible to further pressure the already tense situation."
Two airports in Crimea have been taken over by soldiers and armoured personnel carriers were seen on the roads as links through the area were shut off to the public.
The Crimean peninsula’s main port, Sevastopol, where Russia’s Black Sea fleet is based, has also been blocked off.
Barack Obama warned Mr Putin that there “will be costs” for any military intervention in Ukraine but did not go into details.
“We are now deeply concerned by reports of military movements taken by the Russian Federation inside of Ukraine,” he added.
“Any violation of Ukrainian sovereignty and territorial integrity would be deeply destabilising, which is not in the interests of Ukraine, Russia or Europe.
“It would present a profound interference in matters that must be decided by the Ukrainian people.”
The local administration in Crimea moved a referendum on whether the Autonomous State of Crimea should have even greater independence forward to 30 March.
It only became part of Ukraine in 1954 when Soviet leader Nikita Khrushchev transferred jurisdiction from Russia, a move that was a mere formality when both Ukraine and Russia were part of the Soviet Union.
The Soviet breakup in 1991 meant Crimea landed in an independent Ukraine.
Additional reporting by Reuters