Sri Lanka's navy sank a Tamil Tiger rebel ship and four smaller attack boats in a battle that killed 20 guerrillas off the northeastern coast early Saturday, the military was quoted as saying by the Associated Press. The naval attack came amid a sharp escalation in the 25-year-old civil war between government forces and the ethnic Tamil rebels. Government troops in recent months have made dramatic progress in fighting the rebels in the north, seizing a series of guerrilla bases and swaths of territory. The sea clash erupted after naval patrol vessels spotted the rebel ship at about 2 a.m. on Saturday some 70 nautical miles off the coast, said navy spokesman Cmdr. Mahesh Karunaratne. He said when navy boats approached the suspicious ship, «it increased speed and tried to flee» while firing. Navy boats retaliated and destroyed the ship in a battle that lasted about two hours, he said. He said the 100-foot (30-meter) vessel was carrying arms and war materials for the rebels. Four boats that came to the support of the ship were also destroyed, he said, adding at least 20-25 rebels were killed. The navy did not suffer casualties, he said. The rebels could not be reached for comment.