Tamil Tiger rebels killed three Sri Lankan navy soldiers on a foot patrol in a firefight near the east coast town of Trincomalee early on Friday, a defence ministry spokesman said.
"Three sailors were killed. They fired with small arms and they were killed near a navy camp at Kuchchaveli," a spokesman for the Media Centre for National Security said.
The attack inflicted "severe damage" on the rebels, known by their official name, the Liberation Tigers of Tamil Eelam, the Centre's Web site (www.nationalsecurity.lk) reported without giving details.
The Tigers, who say they are fighting to create an independent state in the north and east of the island for ethnic minority Tamils, could not be reached for comment.
Since 1983, the war in Sri Lanka has killed some 68,000 people, including more than 4,000 since late 2005. The near daily air, land and sea battles of the past 16 months have left a 2002 ceasefire agreement in tatters.
Friday's incident happened just hours after authorities temporarily closed the Colombo international airport, cut power to the city and fired anti-aircraft guns skyward after reports of suspicious planes flying along the coast toward the capital.