Ukraine accused Russia on Saturday of sending thousands of extra troops into Crimea as the Kremlin vowed to help restore calm on the flashpoint peninsula and Washington warned of "costs" to Moscow should it use force.
Defence minister Igor Tenyukh told the Ukrainian government's first cabinet session that Russia's armed forces had sent in 30 armoured personnel carriers and 6,000 additional troops into Crimea in a bid to help local pro-Kremlin militia gain broader independence from the new pro-EU leaders in Kiev.
Tenyukh accused Russia of starting to send in these reinforcements on Friday "without warning or Ukraine's permission."
The defence chief spoke as dozens of pro-Russian armed men in full combat gear patrolled outside the seat of power in Crimea's capital Simferopol, a day after similar gunmen seized control over airports and government buildings in the territory.
The rugged peninsula jutting into the Black Sea — host to a Kremlin fleet and with an ethnic Russian majority — has now effectively been cut off from mainland Ukraine, with airports shut down and a pro-Kremlin militia establishing a tightly-controlled checkpoint on the main road from the mainland.
Crimea has come to the fore of a Cold War-style confrontation between the West and Russia over Ukraine, a faceoff that has also exposed the ancient cultural rifts between the pro-European west and Russian-speaking south and east of this country of 46 million.
Nowhere has that divide been more apparent than in Crimea — a Black Sea peninsula of nearly two million people that has housed Kremlin navies for nearly 250 years and which a Soviet leader gifted to Ukraine when it was still a part of the USSR in 1954.
Pro-Russian gunmen seized Crimea's government and parliament buildings in Simferopol on Thursday before allowing lawmakers to appoint a new prime minister and call for a regional referendum — moved forward on Saturday to March 30 — that would proclaim even greater independence for the already-autonomous region.
Dozens of soldiers with no insignia but dressed in Russian battle fatigues and armed with Kalashnikovs then seized Crimea's main airport in Simferopol and Ukraine's Belbek military air base near Sevastopol — home of Russia's Black Sea Fleet.
Crimea's newly-chosen prime minister followed that up on Saturday by fervently calling on Russian President Vladimir Putin to help restore "peace and calm" amid his standoff with Kiev's Western-backed authorities.
"Taking into account my responsibility for the life and security of citizens, I ask Russian President Vladimir Putin to help in ensuring peace and calm on the territory of Crimea," Sergiy Aksyonov said in an address broadcast in full on Saturday by Russian state television.
Aksyonov also said that all of Crimea's security forces — including the regional armed forces and police — would now be subordinate to him.
"All those who do not agree, I ask to leave the service," Aksyonov said in the address.
A source in the Kremlin administration soon told Moscow's three main news agencies that "Russia will not leave this request without attention."
The ex-Soviet country's bloodiest crisis since its 1991 independence erupted in November when ousted president Viktor Yanukovich — who has since fled to Russia — rejected an historic deal that would have opened Ukraine's door to eventual EU membership in favour of tighter ties with old master Moscow.
A week of carnage in Kiev claimed nearly 100 lives last week.
Gazprom warns Ukraine
Ukraine's interim president Oleksandr Turchynov had made his own dramatic appeal to Putin late on Friday as the pace of Russian troop movements intensified around their bases and armoured personnel carries patrolled Simferopol's main streets.
"I personally appeal to President Putin to immediately stop military provocation and to withdraw from the Autonomous Republic of Crimea," a sombre Turchynov said on national television.
"It is a naked aggression against Ukraine."
Western governments have been watching with increasing alarm as Kiev's new rulers grapple with the dual threats of economic collapse and secession by Russian-speaking regions that had backed Yanukovich.
But the more immediate threat of a debt default that Kiev leaders warn could come as early as next week looked even more ominous when Russia's state-owned Gazprom — often accused of being wielded as a weapon by the Kremlin against uncooperative ex-Soviet states — warned that it may be forced to hike the price it charges Ukraine for natural gas.
"The debt is $1.549 billion, it is huge," Gazprom spokesman Sergei Kupriyanov told the RIA Novosti news agency.
"Clearly, with this debt Ukraine may not be able to keep its discount (to market price) for the gas. The agreements on the discount forsee a full and timely payment."
Ukraine won a one-third discount from Gazprom under a deal signed by Yanukovich with Putin that also saw Russia promise to buy $15 billion in the Kiev government debt.
But Russia has only bought $3.0 billion in Ukrainian obligations and has effectively frozen further deliveries of aid.
Ukraine's new leaders have said that the economically-teetering country needs $35 billion over the coming two years to keep the economy afloat.
Obama to skip Russia summit?
Ukraine had filed a formal protest on Friday after claiming that Russian helicopters had entered its airspace as part of snap military drills involving 150,000 troops that Putin had ordered in a region bordering Ukraine last week.
The UN Security Council discussed the crisis behind closed doors while US President Barack Obama -- although not referring to Russia directly -- warned that "there will be costs for any military intervention in Ukraine."
"We are now deeply concerned by reports of military movements taken by the Russian Federation inside of Ukraine," Obama said in a hurriedly scheduled statement at the White House.
A senior US official separately said Obama and some key European leaders could skip June's G8 summit in Sochi if Moscow's forces became more directly involved in Ukraine.
The foreign office said British foreign secretary William Hague will arrive in Kiev on Sunday for talks with the new government.
Polish foreign minister Radoslaw Sikorski — a top proponent of Ukraine's future EU membership — also cut short a visit to Iran to handle the deepening crisis.