A fierce battle between the navy and Tamil Tiger rebels has taken place off Sri Lanka's northern Jaffna peninsula.
The navy says it has sunk 22 rebel boats and lost two of its own. At least 20 sailors are missing, while the rebels say they lost five of theirs.
The rebels told the BBC they sank two navy boats and badly damaged another.
Both sides blame the other for starting the battle, which came a day after heavy army shelling killed dozens of refugees in the east of the island.
Nearly 3,000 people have been killed in fighting since late last year, the government says.
The defence ministry said on its website that the rebels had attacked naval vessels in an attempt "to disrupt the supply of essential items to the Jaffna peninsula".
It said "suicide cadres" were on board the rebel boats and accused them of seeking to sink a passenger ship carrying 300 civilians from Trincomalee to Jaffna.
Military spokesman Prasad Samarasinghe said air support had been called in after the rebels attacked near Mullaitivu.
"They are trying to rescue the navy sailors. There are survivors," he told Reuters news agency.
The rebels, meanwhile, say their vessels were conducting exercises when they were attacked by the navy.
"We were forced to retaliate to safeguard our trainee boats," a spokesman, Rasaiah Ilanthiraiyan, told the BBC Tamil service.
The rebels deny trying to attack a passenger ferry, and say no such vessel was in the area.
They say at least 25 sailors were killed in the clash. Four others were captured alive, and the body of another was recovered.
The Tamil Tigers say they are prepared to return the body of the dead sailor to the Red Cross on Friday. The four captured sailors will be handed over to ceasefire monitors.
No monitors present
The monitors are unable to confirm any of the details of the battle.
Their staff stopped travelling on navy boats earlier this year after the rebels said they could not guarantee their safety.
Government forces and rebels have frequently clashed on land and at sea this year as a threadbare ceasefire has unravelled.
Last month, the rebels carried out a suicide attack on a naval installation at the port of Galle, a popular southern tourist destination.