Tamil Tiger rebels in a boat fired at a Sri Lankan navy post in the port town of Trincomalee on Thursday but retreated when the navy retaliated with gunfire, a navy spokesman said.
The incident comes ahead of a visit by Norwegian peace envoys next week.
The navy suffered no casualties, but it was unclear if any of the rebels were hurt, said navy spokesman Commander D. K. P. Dassanayake.
"They first fired grenades from launchers and then used automatic weapons," Dassanayake said. "In self defense, we retaliated."
Rebel representatives could not immediately be reached for comment and there was no report on the rebels' Web-sites.
Trincomalee town and its port are under government control, but the rebels have their presence around.
Norwegian Minister of International Development Erik Solheim, whose peace efforts led to a 2002 cease-fire in Sri Lanka, is scheduled to visit Colombo April 6 to meet with President Mahinda Rajapakse, the Norwegian Embassy said in a statement.
Solheim's trip will be preceded by a visit by another peace envoy, Jon Hanssen-Bauer, starting Monday. He will look after the day-to-day issues relating to the peace process.
The truce has come under severe strain due to spiraling violence, with more than 166 people, including 87 government security personnel, killed since December, reports the AP.
The United States does not recognize the entry of Ukrainian territories into Russia. Such a development will seriously complicate prospects for a diplomatic settlement