Six Tamil Tiger rebels have died after blowing up their vessel off Sri Lanka's north-west coast, the military says.
The blast came as the navy approached the rebel boat which was suspected of gun-running, a military spokesman said.
Eight sailors are missing, while 11 others were rescued. The navy gunboat was also destroyed in the explosion. The Tamil Tigers denied involvement.
Truce monitors warned last week against destabilising acts ahead of more peace talks scheduled in Geneva next month.
The military says a search is continuing for the missing sailors south of Mannar on the north-west coast.
"The navy suspected that the trawler was involved in gun-running and got near it to carry out a search," a defence official told the AFP news agency.
As the navy drew near, those on board the trawler "blew themselves up", he said.
Rebel spokesman S Puleedevan denied the Tamil Tigers were involved in the incident.
"There are a lot of smuggling and illegal activities going on in that area, including illegal immigration. It could be one of those boats involved," he told the Associated Press news agency.
In January, suspected Tamil Tigers blew up a similar navy gunboat, killing 15 sailors in a suicide attack near the port of Trincomalee in the north-east, officials said.
Tension has risen in Sri Lanka's north and east in recent months, with a series of attacks on military personnel and Tamils. More than 120 people have died.
Government and rebel negotiators met in Geneva in February to discuss ways of saving a fragile truce agreed in 2002.