The Sri Lankan navy says it has destroyed much of the Tamil Tiger's arms smuggling network after sinking three large ships.
One of the ships the navy says it destroyed
The vessels have been sunk in three different encounters since Monday morning, Vice Admiral Wasantha Karannagoda said.
There has been no word from the Tigers on the incidents.
The military have made advances against the rebels in the east of the country in recent months.
The Tamil Tigers still control large parts of the north.
The confrontations took place more than 1,200km (750 miles) off Sri Lanka's south-east coast in a remote part of the Indian ocean.
Vice Admiral Karannagoda says the Tigers have been badly hit
"The loss of the ships will have a huge impact on the Tamil Tigers," Vice Admiral Karannagoda told the BBC.
"Their abilities are 90% destroyed with these vessels going down."
The incidents at sea come as both sides appear to be gearing up for the next stage of Sri Lanka's renewed civil war, says the BBC's Roland Buerk in Colombo.