Sri Lanka's navy and air force on Saturday destroyed three Tamil Tiger gunboats off the country's northwestern coast, killing at least 15 rebels, while a roadside blast killed four soldiers, military officials said. "Our radars detected two Tiger (rebel) boats approaching our shores and we dispatched navy boats to confront them," navy spokesman, Commander D.K.P. Dassanayake said of the sea battle that started just after dawn Saturday. As the navy boats drew closer, seven more boats from the Tamil Tigers' sea wing, the Sea Tigers, entered the fray, Dassanayake said of the incident off the coast of Mannar. "Our sailors managed to completely destroy two Tiger boats and we estimate that 15 men would have been on board and killed," Dassanayake said. Four Sri Lankan sailors were also wounded, Dassanayake said. Air force planes destroyed a third boat, Dassanayake said. He had no details of casualties in the third attack. The fate of six remaining boats that withdrew was not known. Also on Saturday, suspected Tamil rebels detonated a roadside bomb targeting a military truck in northern Sri Lanka killing four soldiers, an official said. The blast in northern Vavuniya district also wounded 18 - three soldiers and 15 civilians an official at the Media Center for National Security said on condition of anonymity citing policy. There was no immediate comment available from the rebels. A rebel official who responded the telephone in the insurgents' headquarters in Kilinochchi said rebel officials were not available to comment. The navy regularly patrols the coasts to detect weapons smuggling by the separatist Tamil Tiger rebels, who are fighting for a separate homeland for 3.2 million ethnic Tamils, accusing the majority Sinhalese of discrimination. The navy has increased patrolling the sea after this week's confrontation with a rebel-hijacked fishing trawler which was smuggling in arms and ammunition. On Tuesday, Sri Lankan navy patrol boats had spotted the fishing trawler off the western shore. When the Sri Lankan naval boats drew close, the men on the other vessel opened fire and threw grenades, forcing the navy to retaliate, killing seven rebels on board, chief government spokesman, Keheliya Rambukwella said earlier. The trawler sank after a huge explosion, suggesting the vessel was carrying arms and explosives, Rambukwella had said. The Tigers have been fighting since 1983 for a Tamil homeland. The rebels have repeatedly been accused by the government of using fishing boats and other small vessels to smuggle weapons to their fighters. Sri Lanka, a small tropical island off India's southern coast, is witnessing increasing violence due to near collapse of a 2002 cease-fire. Even though both sides have not officially withdrawn from the truce renewed violence since last December killed more than 3,200 combatants and civilians.