COLOMBO, Sri Lanka (AP) _ Separatist rebels besieged an important military base Sunday, claiming they killed 1,000 government troops in one of the biggest battles of Sri Lanka's 13-year civil war.

The Tamil guerrillas said they had destroyed the Mullaittivu base and were hunting down a small number of troops who were still hiding outside the camp.

``One thousands troops have perished,'' said a statement issued by the rebels' London office, which admitting losing 120 of their own men.

An air, land and sea battle has raged since Thursday in northern Sri Lanka, at a base 170 miles north of the capital, Colombo.

Sri Lanka's navy brought in hundreds of soldiers Sunday and evacuated injured commandos who had been sent in earlier to rescue their colleagues at the base, military officials said, speaking on condition of anonymity.

They've established a foothold a few miles from the base, they said. Further details were not immediately available.

Maj. Tilak Dunuwille, a defense ministry spokesman, said 211 soldiers and sailors and 425 rebels have been killed defending the base.

But other military officers, speaking on condition of anonymity, said the number of soldiers killed was far higher. The base had 1,200 personnel.

It was impossible to reconcile the rival claims. The government bars reporters from the turbulent north, and there was little communication from the camp.

The rebels claimed to have shot down a military helicopter on Saturday, carrying 37 soldiers being sent as reinforcements to lift the siege on the camp. The military denied that a helicopter was brought down, but said that a chopper was hit and managed to return to a nearby army camp.

The rebels have prevented two groups of commandos from joining up and reaching the camp. The soldiers have been encircled by the rebels, who were raining down mortars on them and attacking in waves, officials said.

Helicopters also dropped ammunition, food and medical supplies for the soldiers, who have been fighting hand-to-hand battles for three days.

A convoy of about 10 to 15 rebel trucks arrived Saturday night at the northern town of Kilinochchi, 30 miles west of Mullaittivu, carrying hundred of bodies of soldiers killed in the fighting.

The biggest previous battle was in November 1993, when 754 soldiers and sailors and 700 rebels were killed in four days of fighting at the Pooneryn-Nagathevanthurai military complex in northern Sri Lanka.