The United Nations on Wednesday pointed the finger at Sri Lankan forces over the killing of 17 French charity workers on the island nine years ago, despite repeated denials by the military.
A UN war crimes report on Sri Lanka said the 2006 attack against Action Against Hunger (ACF) staff was "the most significant case of humanitarian workers killed" in the country.
"Based on the information (the investigation) has compiled, there are reasonable grounds to believe that members of the security forces committed the extrajudicial executions of the ACF staff," the report said.
It is the first time a UN organisation has placed blame for the aid workers' deaths on Sri Lankan forces, which have long denied carrying out the killings while battling Tamil Tiger rebels.
Previous Sri Lankan investigations into the ACF attack have been inconclusive, and the UN said security forces intimidated the victims' relatives whenever international attention was paid to the case.
The ACF, which pulled its aid workers from the embattled country after the loss of its staff, maintained that only an independent international investigation could lead to prosecution of the killers because Sri Lanka's military denied involvement.
The UN also said in the report it believed security forces were responsible for the death of five Tamil students gunned down in the town of Trincomalee seven months before the attack on ACF.
The long-awaited report, covering a nine-year period before and after the end of the civil war in May 2009, detailed horrific abuses committed during the conflict, including war crimes and crimes against humanity.
Sri Lanka's new unity government has promised dramatic reforms to achieve accountability for alleged atrocities during the war with the Tamil Tiger guerrillas, in which 100,000 people died.
However, the new administration of President Maithripala Sirisena has stopped short of agreeing to an investigation involving international experts as recommended by the UN.