A French charity accused the Sri Lankan government of "lacking the will to establish the truth" about the massacre of 17 aid workers in 2006 and called for an international inquiry.

Seventeen mostly Tamil staff members of the charity, Action Contre la Faim (ACF), were shot dead in the ACF compound on August 4 2006 in the northeastern town of Muttur, near where fighting was taking place between the government and Tamil Tigers.

"Today, nearly 3 years after the crime, one has to recognize that these procedures have failed, and that the Sri Lankan government obviously lacks the will to establish the truth," the French charity said in an emailed statement on the report on Saturday July 18.

"In light of this, Action Contre la Faim (ACF) reiterates its call, notably to the European Union, to constitute an international inquiry into this massacre."

“ACF has closely followed three separate judicial proceedings. Two years into these investigations, the search for truth has been a casualty of obstructionism, the intrusion of politics into the judicial process, a lack of transparency, and even errors,” the statement said.

“The massacre is the gravest crime carried out against a non-governmental organization and is comparable to a war crime under international law,” it added.

The head of a presidential probe into rights abuses, including that massacre, said in a report early this month that his work was hampered by the lack of witness protection and the abrupt winding-up of his investigation.

Thirteen men and four women who worked on water sanitation and farm projects for ACF were found shot dead in an area where government troops and Tamil Tigers were locked in combat.

Nordic peace monitors at the time blamed the killings - the worst attack on aid workers since the bombing of the UN headquarters in Baghdad in August 2003 - on government forces.

The government has denied any role.

The report by the commission of inquiry appointed by President Mahinda Rajapaksa to investigate serious human rights abuses is inconclusive about who killed the aid workers.

The Island and the Daily Mirror newspapers quoted from the commission report, which had not been made public by the authorities yet.

The Island newspaper said the inquiry accused the ACF of "gross negligence" and recommended that the charity pay 10 years' salary to the families of the victims.

The commission, headed by retired judge Nissanka Udalagama, has been dismissed by rights activists as a government cover-up.

Foreign observers to the panel two years ago predicted the commission would fail to find anything substantive and quit last year, saying it did not meet international standards and had been interfered with politically. The government denies that.

The commission's mandate was not extended when it expired in June, making it the latest in Sri Lanka's long history of probes into rights abuses that were incomplete or inconclusive.

"We have not been able to complete the whole thing because we didn't have the video conferencing facility and a witness protection bill...is still in parliament," retired Supreme Court Judge Nissanka Udalagama told Reuters.

A number of witnesses have fled the country in fear for their lives, and video-conferencing was needed to contact witnesses who live abroad, he said.

Udalagama, head of the eight-member commission, said they could have called other witnesses but the president wanted a report based on what had been done so far.

The report exonerates the army and navy, but says auxiliary police known as home guards could have carried out the killings. "There was other evidence like the presence of Muslim home guards. They had access to the weapons. And it could have been LTTE," Udalagama said.

It was the latest of many Sri Lankan investigations of rights abuses that were incomplete or inconclusive.

Rights watchdogs have reported hundreds of abductions, disappearances and killings, blamed on both the government and the LTTE, throughout the course of Sri Lanka's 25-year civil war, which ended in May.

The country has a long history of failing to prosecute rights abuses, particularly when members of the security forces are involved, going back to the early 1970s when the government violently suppressed a Marxist insurrection.