The bodies of 17 employees of French charity Action Against Hunger (Action Contre la Faim, ACF) were brought to the main hospital in Trincomalee as heavy gunfire boomed in the distance.

The battle for access to water from a disputed irrigation dam in northeastern Trincomalee district has raged for two weeks, leaving at least 440 people dead by official count.

The defence ministry said that security forces were keeping up "Operation Watershed" to lift the rebel blockade which has deprived water to some 15,000 farming families.

The aid workers were killed when the fighting which began near the irrigation dam spread to the coastal town of Muttur, where a major battle erupted last week.

An airforce trooper was killed in a suspected Tiger attack Tuesday while three people who escaped with injuries were brought to the same hospital where the bodies of the aid workers were being identified, officials said.

"We will have the autopsies (Tuesday) and release the bodies for the funerals," a hospital official said. "It is likely that there will be several funerals held together, but it is up to the next of kin to decide."

The ACF on Monday suspended its mission to Sri Lanka following the killings, the worst against the charity since its inception 25 years ago.

"These humanitarian workers were clearly identified by their T-shirts as members of a non-governmental organisation," said the group's director Benoit Miribel.

Aid officials said they were not in a position to say how the staffers had been killed, but several witnesses who saw the bodies Sunday said they had been shot dead.

A resident who saw the bodies told AFP that it appeared that the aid workers had been machine-gunned while at work in their office located next to the hospital in Muttur. The hospital was also hit by shells.

"There is no evidence whatsoever at present," Police Inspector General Chandra Fernando said in a statement.

"The police will, however, be able to submit a detailed report subsequent to an autopsy."

The rebel Liberation Tigers of Tamil Eelam (LTTE) and government forces have blamed each other for the killings.

Human Rights Minister Mahinda Samarasinghe said Colombo would ensure a "clean" investigation into the bloodiest attack against a humanitarian organisation in the island's three decades of conflict.

Former US president Bill Clinton, who is a UN special envoy on tsunami recovery efforts in the Indian Ocean, expressed shock at the killings.

The deaths, which came amid heavy fighting in this coastal district, also marked a new low in the island's faltering peace process.

The United States, a key backer of Sri Lanka's Norwegian-led peace process, said it was looking for a way to stop the bloodshed.

"It's a terrible situation and we're quite disturbed by the descent into violence," US State Department spokesman Sean McCormack said.

"We're going to do what we can to try to bring at least a return to an end to the violence and then, ultimately, go down the road of any negotiations that would bring a permanent end to the violence."

An estimated 60,000 people have been killed since the Tamil insurgency began in 1972.

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