A French aid agency said it was trying to find out who shot dead 15 of its employees in northern Sri Lanka but that government troops had sealed off the scene of the massacre.
The bodies of 11 men and four women, all wearing Action Against Hunger (ACF) T-shirts, were found face-down in their office on Sunday in the town of Muttur, close to heavy fighting between troops and Tamil Tiger rebels.
The rebels have accused the security forces of killing the aid workers, who were all members of Sri Lanka's minority ethnic Tamil community.
Benoit Miribel, the director general of Action Against Hunger (ACF), said his organisation was stunned by the killings which were unprecedented in the organisation's 25-year history.
"We are trying to send a team to find out what is going on in this area," Miribel told AFP in Paris. "But soldiers have prevented us from entering the town which remains completely sealed off."
He said the organisation urgently wanted "to go to our offices there to retrieve the bodies and carry out an investigation to find out who was responsbile."
Miribel said ACF, which has nearly 250 staff in Sri Lanka working on tsunami relief programs, had no plans to leave the troubled northeast.
Heavy fighting broke out in Muttur and the surrounding northeastern district of Trincomalee last month after the government accused the Liberation Tigers of Tamil Eelam (LTTE) of blocking a key waterway.