The Sri Lanka navy sank two Tamil rebel boats in a pre-dawn skirmish on Wednesday in waters off the country's northern Jaffna peninsula, military officials said.
They said a navy patrol ran into a cargo convoy of the Liberation Tigers of Tamil Eelam (LTTE) near Jaffna's Point Pedro harbor.
"Two of the boats blew up and sank when the navy opened fire, a clear indication that they were transporting explosives," a military spokesman.
He said two other rebel craft were also badly damaged, but he could not confirm whether they had sunk. He did say however, that the navy patrol had returned to port without any casualties or damage.
The LTTE, which has been fighting since 1983 for a separate minority Tamil state in the country's north and east, has declared a unilateral ceasefire to push forward a Norwegian peace initiative.
The government had refused to match the truce, which expires on Saturday, but the battlefields have been largely quiet this month amid intense diplomatic efforts to begin talks on a settlement to a conflict that has claimed some 64,000 lives.