At least 51 Sri Lankan soldiers and sailors were missing and feared dead after Tamil Tiger rebels rammed explosives-laden boats into two naval ships off the north coast, military officials said on Monday.

The Defense Ministry said in a statement a navy convoy was attacked by some 10 to 12 Liberation Tigers of Tamil Eelam boats off the Jaffna peninsula on Sunday evening."During the confrontation SLNS Pabbatha was hit by a suicide boat and sank," the statement said, adding that the ship had a crew of 25 sailors and 58 soldiers.

"Naval craft Valampuri with a crew of 25 naval ratings has lost communication" since the attack, the statement said. "So far 43 soldiers and 14 naval ratings have been rescued."

The remaining 51 were missing and naval ships were combing the area for possible survivors, military officials earlier said.

They said the rebels used at least three or four fiberglass boats loaded with explosives to ram the ships.

The guerrillas' naval wing, called the "Sea Tigers," usually uses fiberglass boats fitted with high-powered motors to evade escort vessels in their attacks against the navy.

The ministry statement said the rebel boats had been engaged by naval escort vessels and other fast attack craft sent to the area soon after the rebels launched the attack.

"Six to eight terrorist crafts were destroyed due to naval gunfire," it said.

Naval officials in the east said they believed at least 20 guerrillas had been killed in the fighting.