The head of a French aid agency says they are "stunned" by the murder of 15 of their workers in north-eastern Sri Lanka over the weekend.
Aid is brought to families in the violence-torn town of Muttur
Benoit Miribel said that members of Action Against Hunger had so far been unable to recover the bodies.
The Sri Lankan government has promised an independent investigation into the killings of the 11 men and four women.
In a separate development, military officials say that a senior policeman has been killed by a bomb near Kandy.
A government spokesman told the Associated Press news agency that Upul Seneviratne, was killed by a "suspected rebel bomb" near the famous Buddhist holy city in the centre of the country.
"By all accounts we have, he was killed by the terrorists," the spokesman said.
Mr Seneviratne was in charge of the Special Task Force, a counter-terrorism commando unit.
The Paris-based Action Against Hunger group (AAH) said that the 15 employees were shot over the weekend in Muttur, where they helped survivors of the December 2004 tsunami and people affected by violence in the country.
Mr Miribel, the Director-General of AAH, said that the charity had not suffered such a loss in its 25 years of existence.
The organisation says that it is now reviewing its presence in the country.
Mr Miribel said the group wanted to send a team to the area but was prevented from doing so by soldiers.
The government has said that it will order a "clean and independent" probe into the killings of the 11 men and four women who worked for AAH.
"We can't come to conclusions right now but if the story is correct, it will be a very high priority investigation," Human Rights Minister Mahinda Samarasinghe told the French news agency, AFP.
Fighting between the army and Tamil Tiger rebels erupted in the Muttur area more than two weeks ago, after the rebels cut the water supply to mostly Sinhalese villages.
The army on Monday is reported to have resumed shelling of rebel positions in the north-eastern district of Trincomalee.
The attacks came despite a Tamil Tiger agreement to allow the reservoir to be reopened and a warning by the rebels that they would regard renewed shelling as a declaration of war.
A pro-Tamil Tiger website blamed the government for the killings but the military rejected the claim.
"We did not have people in the area at the time they were supposed to have been killed," military spokesman Upali Rajapakse told the AFP news agency.
The Tigers on Monday said they had offered "unconditionally" to re-open a sluice gate to let water through to farmers in government-controlled lands.
Recent fighting in the Trincomalee area has been fierce
The head of the rebel movement's political wing, SP Thamilselvan, said the government's decision to resume shelling on Sunday was "a declaration of war".
The Muttur fighting has been some of the island's fiercest since the signing of a ceasefire agreement four years ago.
The government says it is committed to the truce but the political situation with the rebels, who want a separate homeland in the north and east, remains deadlocked.
About 60,000 people have died since the rebel insurgency started three decades ago.