COLOMBO, Aug 13 (Reuters) - Three Tamil Tiger rebels and a soldier were killed in Sri Lanka's northeast and the Navy sank a rebel vessel, the military said on Monday after overnight land and sea battles.

The clashes on and off the coast of Pulmoddai in the northeastern district of Trincomalee were the latest in a quickening of the two-decade civil war that has killed around 4,500 people since last year alone.

"Troops have confronted Tigers trying to flee from the east to the north and killed three of them. One soldier was also killed in action," a spokesman for the Media Centre for National Security said, asking not to be named, in line with policy.

"Then the navy encountered a cluster of rebel boats which we think had come to ferry the fighters on land to the north, and sank one boat and damaged several others."

The Liberation Tigers of Tamil Eelam, who are seeking to carve out an independent state in north and east Sri Lanka, were not immediately available for comment.

The latest clashes came after rebels killed four soldiers with a roadside bomb in the island's far northern peninsula of Jaffna on Sunday and a civilian with mortar fire in a separate attack in the north, the military said.

Nearly 70,000 people have been killed since the war erupted in 1983.

Fighting between the state and rebels is now focused in the north after the military evicted the Tigers from their last stronghold in the east. However, analysts see no clear winner on the horizon and fear the fighting could grind on for years.

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