* Move announced after weeks of Russian pressure on Ukrainian bases

* Turchinov says Russian forces threatened servicemen and their families

* But says Ukrainian forces performed nobly

* Russians use helicopters, stun grenades, machine guns to take marine base (Releads with withdrawal announcement)

By Aleksandar Vasovic and Gabriela Baczynska

FEODOSIA/SIMFEROPOL, Ukraine, March 24 (Reuters) - Ukraine announced the evacuation of its troops and their families from Crimea on Monday, effectively acknowledging defeat in the face of Russian forces, who stormed one of the last remaining Ukrainian bases on the peninsula.

Thousands of Ukrainian troops have been besieged on bases in Crimea, offering no armed resistance but refusing to surrender, since President Vladimir Putin declared Moscow's right to intervene at the start of the month.

Moscow formally annexed the region last week and its forces have been seizing the last Ukrainian bases in recent days.

"The National Defence and Security Council has instructed the Defence Ministry to carry out a re-deployment of military units in Crimea and evacuate their families," acting president Oleksander Turchinov told parliament in Kiev.

The move, he said, had been made following threats by Russian forces on the lives and health of Ukrainian service staff and their families.

Russian forces, using stun grenades and machine guns and backed by two helicopters, swept into a marine base in the port of Feodosia early on Monday, overrunning one of Ukraine's last symbols of resistance. Ukrainian officers were taken away for questioning, Ukrainian officials said.

An official withdrawal from the base was due to start at 3 p.m. (1300 GMT), Ukrainian military spokesman Vladislav Seleznyov said.

Ukrainian flags were taken down inside the base. Russian forces used similar tactics to take Ukraine's Belbek air base in Crimea on Saturday.

Russia's seizure of Crimea after the ousting of Ukraine's pro-Russian president by mass protests in Kiev has triggered the worst East-West crisis since the Cold War.

Moscow formally annexed Crimea on March 21, five days after newly-installed pro-Russian leaders held a referendum which yielded an overwhelming vote to join Russia. The West and Kiev say the referendum was illegal and the result.

Russian forces captured part of the Feodosia base, used by the 1st Separate Marine Battalion, Ukraine's top military unit, earlier this month. Ukrainians had kept control of the armoury, the barracks and other facilities.

Turchinov, putting a brave face on Ukraine's inability to defend its bases, said Ukrainian troops' refusal to surrender in Crimea had bought valuable time for the armed forces to re-group nationally to protect the rest of Ukraine.

"Despite the huge losses, Ukrainian forces in Crimea have fulfilled their duty. They provided the ability and time for the Ukrainian armed forces to be able to ensure defensive preparations and for partial mobilisation to be organised."

BASE TAKE-OVER

A Ukrainian army officer, First Lieutenant Anatoly Mozgovoy, told Reuters by phone from inside the compound that the Russians had fired shots while the Ukrainian soldiers were unarmed. Asked if the base had been taken over, he said: "Yes".

"The interior of the compound is full of Russian troops," Seleznyov, a Ukrainian military spokesman in Crimea, said earlier on Monday, adding that the Russians were taking away Ukrainian officers for questioning.

The Defence Ministry also said Russians had driven away Ukrainian marines in trucks from the base.

"Currently, between 60 and 80 Ukrainian marines are detained and in practice held captive by the Russian military on the territory of the Feodosia sea port. They are subject to constant psychological pressure," the ministry said,

Two days after the Belbek storming, the commander of the airbase, Colonel Yuliy Mamchur, has yet to be freed. His aides believe he is being held in the Russian Black Sea Fleet's home town of Sevastopol.

Ukrainian forces also abandoned a naval base after attacks by pro-Russian protesters, and had to surrender two flagship vessels to Russian forces over recent days as Moscow solidified its grip on Crimea. (Additional reporting by Natalia Zinets in Kiev; Writing by Richard Balmforth; Editing by Peter Graff)

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