By Roland Buerk
BBC News, Colombo
Sri Lanka's navy says it has sunk two cargo vessels at sea.
A spokesman said both the ships, which were off the country's south-east coast, were believed to be carrying weapons for the Tamil Tigers.
The incidents come as battles on land intensify between government forces and the rebels fighting for a separate state in the north-east.
Despite a ceasefire still being in place on paper, the island is sliding back towards a full-scale civil war.
The first vessel was spotted during the night by navy patrol craft.
The 70-metre-long (229ft) ship was challenged and warning shots were fired across her bows. But the crew fired back and a battle followed.
There were large explosions on board the ship before the vessel sank.
After the skirmish, the navy patrol came across a similar ship nearby that also ignored orders to stop for an inspection.
After warnings, it was destroyed too.
Navy spokesman Lt Cdr Rohan Joseph said he believed both vessels were carrying weapons for the Tamil Tigers.
The incidents at sea come as Sri Lanka's military is moving to take remaining pockets of the eastern province still held by the Tigers.
More than 40,000 people have fled their homes in the district of Batticaloa.
The Tigers have said the armed forces have made several attempts to storm their defensive lines in the north of Sri Lanka but have been beaten back.
The ceasefire that has been in place since 2002 is being ignored by both sides.
A senior defence official has said the fighting could last for another two to three years and he said the government was confident it could defeat the Tigers on the battlefield.