Sri Lanka's navy says it has sunk two Tamil Tiger boats off the north-western coast, killing nine rebels.
The navy said both craft had gone down with all crew near Kalpitya. Pro-rebel website TamilNet said eight fishermen were reported missing in the same area.
The sinking of the boats came on the fifth anniversary of a ceasefire, which has unravelled over the past year.
More than 4,000 people have died since late 2005. The rebels have said they are compelled to renew their struggle.
A Sri Lankan navy spokesman told the Reuters news agency that one of the craft sunk near Kalpitya, off the coast of Putallam about 120km (75 miles) north of Colombo, was fitted with heavy weapons.
"The vessels were definitely the Tigers," he said, adding that "nine of their cadres were killed."
TamilNet had a different version.
"Eight fishermen who left from Kalpitya to go fishing in their boats on Wednesday evening are reported missing," it said.
In a message released on the truce anniversary, the Tamil Tigers said the peace process had "virtually collapsed".
"The Sri Lankan government's ongoing war of aggression has compelled the Tamil people to resume their freedom struggle," the Tigers said.
At least 64,000 people have died since the rebels began their fight for independence more than 20 years ago.
The independent Sri Lankan Monitoring Mission says that 4,000 people have died in the past 15 months, as compared to 130 dead in the previous three years following the truce deal.