Ulf Henriksson, head of the Sri Lanka Monitoring Mission (SLMM), said the Maavilaru dam was just minutes away from being re-opened, returning water supplies to thousands of families, when the bombardment started.

"No water. War instead of water. Not a good idea, not a good solution," Henriksson told the BBC in comments reported Monday.

"... we could have waited some minutes more for the water so I think (the attack) was a bad idea," he said.

At least 425 people have died in clashes over the Maavilaru dam in the northeastern district of Trincomalee since July 26 after the government accused rebels of blocking the waterway, cutting off supplies to thousands of families.

The guerrillas said residents closed the waterway, which lies in rebel-held territory, to get the government to improve their drinking water supply.

A spokesman for the Liberation Tigers of Tamil Eelam (LTTE) said the monitors had a "narrow shave" in the shelling.

"We had informed the Sri Lankan government and clearance was obtained," S. Puleedevan told AFP. "But, as they approached the area, there was heavy shelling and they can't open the sluice gates. Even the monitors had a narrow shave."

The government said it was not involved in talks between peace-broker Norway and the rebels on re-opening the dam.

"Water should not be a negotiating tool," Colombo spokesman Keheliya Rambukwella told AFP. "We don't want terrorists to come and open the waterway. They must simply allow irrigation engineers to do it, otherwise we will open it anyway."

It has been the worst fighting in Sri Lanka since a truce was agreed in 2002. An estimated 60,000 people have been killed since the Tamil insurgency began around three decades ago.

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