A suspected separatist rebel boat carrying explosives blew up on Saturday, apparently killing at least four men on board, a Sri Lankan defense official said.

Navy patrol crafts spotted a suspicious fishing vessel and went to investigate in the sea of Talaimannar, 155 miles northwest of Colombo, when it exploded, military spokesman Brig. Prasad Samarasinghe said.

"Definitely there would have been explosives, otherwise there wouldn't have been such a big blast," he said.

He said the boat was believed to belong to the rebel Liberation Tigers of Tamil Eelam.

At least four men were seen on board the vessel and all are believed to be dead, Samarasinghe said, adding one navy sailor was injured in the blast.

Daya Master, a rebel spokesman, declined comment on the explosion.

The incident comes as the government and Tamil Tiger rebels prepare to attend peace talks in Switzerland on Feb. 22-23 to try to save a four-year-old cease-fire which has come under threat recently because of frequent violence.

The government and the rebels signed a cease fire in February 2002, which ended nearly two decades of civil war which killed 65,000 people.

The rebels fought to create a separate state for minority Tamils, accusing majority Sinhalese-dominated state of discrimination.

About 81 government security personnel have been killed in attacks blamed on the Tigers since December, and the rebels accuse the government troops of harassing and killing Tamils civilians.