``In one of the worst Tamil Tiger attacks, LTTE Sea Tigers early this morning ... blew up a Naval vessel Fast Attack Craft,'' a statement posted on the army's Web site said.

The Tamil Tigers carried out several attacks against naval vessels using explosives-packed fishing boats before a cease-fire in 2002 halted the rebels' two-decade independence war.

A similar attack in Trincomalee harbor in 1995 triggered full-scale hostilities, dashing a brief truce.

The chief of the Norwegian-led Sri Lanka - Monitoring Mission, Hagrup Haukland, expressed regret over the incident and said he was awaiting further details.

The insurgents want a separate Tamil state, saying discrimination by the majority Sinhalese, who number about 14 million.

Trincomalee, which has a strategic port and a base for the Sri Lankan navy, has been tense this week after five ethnic Tamils died. The military has said the men accidentally blew themselves up in a botched grenade attack on a military patrol, but the rebels said the men came under attack from government forces.

A formal government inquiry has been ordered into the killings.

The Norwegian official who brokered the 2002 cease-fire, Erik Solheim, is scheduled to visit Sri Lanka - in late January to see if talks can start.

U.S. Undersecretary of State Nicholas Burns also plans to visit Sri Lanka - to encourage negotiations between the two sides, State Department spokesman Sean McCormack said Friday. No date for the trip has been announced.

Violence has worsened in the country since November's election of Sri Lanka - 's new president, Mahinda Rajapakse, who campaigned on a promise to take a tough line in negotiations with the rebels. Rebel leader Velupillai Prabhakaran has warned the Tamil Tigers would intensify their struggle if their grievances were not addressed.

The 2002 cease-fire halted two decades of a civil war that has killed more than 65,000 people since 1983. But last month 45 soldiers were killed and 71 wounded in ambushes blamed on the rebels; government troops killed seven suspected rebels.

The two sides have also traded accusations about the slaying of a pro-rebel lawmaker at Midnight Mass on Christmas Eve. And in August, former Foreign Minister Lakshman Kadirgamar was assassinated by suspected Tiger gunmen.

Discuss this story Published: Sat Jan 7 00:30:26 EST 2006

Elsewhere, suspected Tamil rebels lobbed grenades at the army positions in the northeast, wounding at three soldiers in violence that threatens the country's 4-year-old cease-fire.

``It was a good find,'' said Brig. Prasad Samarasinghe, the military spokesman, of the Claymore mines found near the eastern town of Batticaloa before they were detonated. ``We alerted out troops and cleared the area,'' he said.

According to the army, the separatist Liberation Tigers of Tamil Eelam are increasingly using Claymores - remotely detonated, aboveground anti-personnel mines designed to fire hundreds of steel balls.

In December alone, at least 23 sailors and soldiers were killed in two separate Claymore attacks by suspected rebels.

In separate attacks blamed on the rebels, three army units came under fire within a span of one hour in the port city of Trincomalee on Thursday night. Three soldiers were wounded, the Defense Ministry said.

Discuss this story Published: Fri Jan 6 07:41:34 EST 2006