The Sri Lankan government has allegedly protected the security forces, who had executed 17 local workers in 2006, a French aid group said.
"Action Against Hunger" accused the security forces of having lined up the victims at their office in the eastern town of Muttur, forcing them to their knees and shooting them in their heads, News.com.au reports.
The group has compiled a report with information implicating army, navy and police personnel and said its sources range from witnesses on the ground, confidential documents and diplomatic contacts.
The group called for an international investigation into the massacre, the report added.