The Sri Lankan navy has said that at least 10 crewmen are missing and one killed when Tamil Tiger separatists sunk a gunboat escorting a passenger ship.

A navy spokesman said the Tigers were targeting the M/V Lanka Muditha ship, coming from the Northern Jaffna peninsula along the east coast, when the army launched a pre-emptive strike.

The passenger ship turned back because of the fighting.

Tamil Tiger radio said that the boats were warships and ships of supply and that two Tigers were killed in the attack.

Government sources say 20 Tigers have been killed and six of their boats destroyed.

Only means of travel available

The Muditha, which then returned to Jaffna, was the only hope for thousands of people looking to travel between the peninsula and the rest of the island.

The main road to Jaffna crosses the Tiger-controlled area and cannot be used.

All civilian flights to and from the peninsula were stopped last month, after a plane with 55 passengers and crew disappeared shortly after take-off.

A report by a leading human rights group recently said all available evidence pointed conclusively to the flight having been shot down by the Tigers off the east coast.

The Tigers had previously said they were opposed to troops being carried in the planes.

They appear to have the same objection to the boat service between Jaffna and Trincomalee which was also used to take troops as well as civilians.

This latest attack will not stop soldiers going to and from Jaffna, but it may mean that thousands of stranded civilians on the peninsula and in Colombo have no hope of moving in the near future.