Crimeans voted in a referendum yesterday on whether to break away from Ukraine and join Russia, with Kiev accusing Moscow of rapidly building up its armed forces on the peninsula in violation of an international treaty.
Ukrainian acting Defence Minister Igor Tenyukh said Russian troop numbers in Crimea were now almost double the level agreed with Moscow, and Kiev's forces were taking "appropriate measures" along the border with Russia.
Tenyukh dismissed any suggestion that a militarily and economically weakened Ukraine might give up in the face of the Russian power. "Decisions will be taken depending on how events unfold. But let me say once again that this is our land and we will not be leaving it," he told Interfax news agency.
Western countries say the vote, which is likely to favour union with Russia, is illegal and being conducted at the barrel of a gun. At the United Nations, 13 Security Council members voted for a draft resolution saying the result should not be recognised internationally, but Moscow exercised its veto while China abstained.
Crimea's 1.5 million voters have two options: union with Russia or giving their region the broad right to determine its own path and choose relations with whomever it wants - including Moscow.
Russia has the right to keep forces on the Black Sea peninsula, including at its naval base in the port of Sevastopol, under a treaty signed after Ukraine gained independence in 1991.
But Tenyukh accused Moscow of going far beyond an agreed limit on servicemen, which he said was 12,500 for 2014.
"Unfortunately, in a very short period of time, this 12,500 has grown to 22,000. This is a crude violation of the bilateral agreements and is proof that Russia has unlawfully brought its troops on to the territory of Crimea," he said.
This figure had risen from 18,400 on Friday. "The Ukrainian armed forces are therefore taking appropriate measures along the southern borders," he said.
Russian President Vladimir Putin has justified his stance on Crimea by saying he must protect people from “fascists” in Kiev who ousted the Moscow-backed Viktor Yanukovich in February following a violent uprising in which more than 100 people were killed.
The protests began when Yanukovich turned his back on a trade deal with the European Union and opted for a credit and cheap oil deal worth billions of dollars with Ukraine’s former Soviet overlord, Russia.
Voters have two options to choose from - but both imply Russian control of the peninsula.
On the surface, the second choice appears to offer the prospect of Crimea remaining with Ukraine.
However, the 1992 constitution which it cites foresees giving the region effective independence within Ukraine, but with the right to determine its own path and choose relations with whom it wants - including with Russia.
The streets of Simferopol have been largely calm in the days leading up to the vote, although the heavy presence of armed men, many wearing black balaclavas, has created an unnerving atmosphere in the normally sleepy town.
On Saturday night, about 30 men in balaclavas carrying automatic weapons barged into the Hotel Moscow, a Soviet-era hotel where many Western reporters covering Sunday’s referendum are staying.
They said they had come to investigate an unspecified security alert and did not threaten anyone, but some witnesses saw it as a move to intimidate journalists.
Crimean Prime Minister Sergei Aksyonov, whose election two weeks ago in a closed session of the regional parliament is not recognised by Kiev, does not officially acknowledge that Russian troops are in control of Crimea - a position also maintained by Moscow.
Thousands of soldiers
But the Russian military, which leases the Crimean naval base of Sevastopol from Ukraine, has done little to hide the arrival of thousands of soldiers, along with trucks, armoured vehicles and artillery.
Masked gunmen surrounding Ukrainian military bases in Crimea have identified themselves as Russian troops.
Adding to tensions on the eve of the referendum, Ukraine’s military confronted Russian forces which crossed Crimea’s regional border on a remote sand spit, some 30 km (20 miles) off the mainland.
Crimea’s separatist government said its own forces had moved to defend a gas pumping station. Ukrainian officials said no shots were exchanged.
What happens to Ukrainian forces in Crimea after Sunday’s vote is one of many unanswered questions. Commanders are nervous about how Russia will go about taking control of military bases where Ukrainian forces are still armed.
Crimean authorities have said Ukrainian servicemen will have the choice of surrendering their weapons and walking away peacefully or joining pro-Russian local forces.
In the run-up to the referendum, the worst violence in Ukraine has been in the east, where acting president Oleksander Turchinov said there had been three deaths in two days.
He also said there was “a real danger” of invasion by Russian troops across the eastern border. The area has a large number of Russian-speakers - significant since Putin has vowed to protect ethnic Russians and Russian-speakers in Ukraine.