The navy says the clash came after a routine patrol
Sri Lanka's navy says it has fought a sea battle with Tamil rebels, a day after what the military described as the heaviest day of fighting in weeks.
It says that seven small Tamil Tiger boats and three larger craft were destroyed in a fierce clash off north-western Sri Lanka.
The navy says that at least 25 rebels were killed in the clash.
The army says 60 rebels and 11 soldiers died in fighting on Wednesday. There is no word from the rebels.
Meanwhile, police say Tamils in Colombo have been ordered to register, amid concerns about security.
The sea battle lasted for three hours, and involved at least 40 boats, according to a spokesman for Sri Lanka's navy, Lt Commander Rohan Joseph.
He said it began as one of the navy's boats was on patrol near the fishing port of Nachchikuda in north-western Sri Lanka. Two sailors sustained injuries, the navy said.
In a separate development, medical authorities told the BBC that three civilians were killed in a mine attack near the town of Kilinochchi.
The BBC's Roland Buerk in Colombo says that government forces are continuing with an offensive to crush the Tigers and end their fight for a separate state for the ethnic Tamil minority.
The rebels have not commented on the latest clashes - and the government has barred journalists from the war zone.
The military has been pushing up the north-western coast, trying to open a land route to the government-controlled Jaffna peninsula.
There were more battles on fronts elsewhere in the north on Wednesday, and the military's spokesman, Brigadier Udaya Nanayakkara, said it was the heaviest day of fighting for weeks.
The military is continuing a major offensive that has, according to Brig Nanayakkara, brought soldiers just 5.5km (3.5 miles) from Kilinochchi town, where the Tigers have their administrative headquarters.
The UN and other aid groups pulled out of rebel-held territory on Tuesday after the government said it could not guarantee their safety.
Meanwhile, a spokesman for Sri Lanka's police, Ranjith Gunasekera, said people who had arrived in the Western Province, including Colombo, from northern districts in the last five years have been ordered to register at a police station on Sunday.
Most affected by the move will be from the ethnic Tamil minority.
Thousands of civilians have been displaced in the north
About 250,000 people have been displaced by the fighting and many are heading to areas still in rebel hands, especially their coastal stronghold of Mullaitivu.
The state-controlled Daily News has quoted Defence Secretary Gotabhaya Rajapaksa as saying the Tigers were using an influx of people to infiltrate the city and launch attacks.
He said those without what he described as "a valid reason" to stay should go back.
The Liberation Tigers of Tamil Eelam (LTTE) have been fighting for a separate Tamil homeland in the north and east for 25 years.
Asked if he planned to obliterate the Tigers, Sri Lanka's President Mahinda Rajapaksa told foreign correspondents on Monday that the military would try, but it would take time.
Human rights groups say that both sides have been responsible for murders and abductions in a war that has killed 70,000 people and is one of South Asia's longest-running and most persistent insurgencies.