COLOMBO: The Sri Lankan navy attacked and sank six Tamil Tiger rebel boats and killed at least 25 guerrillas during a pre-dawn sea battle on Wednesday, a navy spokesman said. Naval craft detected the boats off the coast of the last remaining patch of territory still with the guerrillas, spokesman Captain D. K. P. Dassanayake said. "There were at least 25 terrorists in the six boats that were sunk," Dassanayake said. "Four of the rebel craft had been packed with explosives for a possible suicide attack against our craft." The navy had stepped up a blockage off the island's northeastern coast amid reports that some of the remaining Tiger leaders may try to escape a military ground offensive. Sri Lanka troops say they are on the verge of defeating the Tamil Tigers, who have been pushed to a small patch of land in the coastal district of Mullaittivu. The rebels are said to be sheltering among some 50,000 civilians allegedly being held by them as a human shield.