Twenty boat people from Myanmar and Bangladesh have starved or dehydrated to death after their wooden trawler stalled at sea a fortnight ago, a group of 71 survivors found adrift off Sri Lanka on Monday told the navy.

Sri Lankan deep sea surveillance vessels intercepted the boat 150 nautical miles off the island's Tamil Tiger-held far north-east in the Bay of Bengal, suspecting it could be transporting rebels fighting a civil war with the state.

The survivors are now being towed to the government-held northeastern port of Trincomalee.

Sixty-seven would-be immigrants originally set sail from Myanmar on Feb 9, stopping in Bangladesh to pick up another 24 passengers, before the trawler's engine failed on Feb 20 en route to Malaysia or Thailand, officials said.

"Obviously these people ran short of food and water," a military spokesman said, declining to be named in line with policy.

"Out of the 91, 3 Bangladeshis and 17 Myanmar nationals have died from starvation and dehydration according to survivors," he added. "So they have thrown the dead bodies overboard."

Local fishermen in deep seas off rebel-held Mullaitivvu district reported the vessel to the navy.

The separatist Liberation Tigers of Tamil Eelam, who are seeking to carve out an independent state in the island's north and east, have hidden among fishing trawlers in past sea clashes with the navy, the military says.