The Group of Eminent Persons has now been subsumed into a wider investigation, the Lessons Learnt and Reconciliation Commission (LLRC), which was officially launched in Colombo on Wednesday amid concerns that it too will fail to fulfill its mandate.

The state department acknowledged such fears in the report, saying that the make-up of the investigating team raises "questions concerning the independence and impartiality of some members of the commission," including CR De Silva, the chairman.

It warns that De Silva's "relationship to the government" and "his involvement in the failure" of the previous commission "could compromise the independence and impartiality" of the new investigation.

The eight-member panel will hear testimony on five separate days in the capital and two days in Vavuniya, near the former war zone, an official statement said.

Allegations dismissed

The LLRC will investigate allegations that Sri Lankan troops committed a range of war crimes during a final assault on the Liberation Tigers of Tamil Eelam (LTTE) in the spring of 2009, when government forces scored a crushing military victory over the Tamil fighters.

"Real progress on justice demands an international investigation."

James Ross, Human Rights Watch legal director

Human rights groups have called for an international investigation into the claims, which have been denied by the government of Sri Lanka.

The government has also dismissed calls for an international inquiry, saying it would be a violation of Sri Lanka's sovereignty and has insisted that its own investigations into the reports are sufficient.

But human rights groups say that the state department report shows that this is not the case, and reiterated their support for an international option.   

"The US state department report shows that nearly 15 months after the war, the Sri Lankan government has accomplished nothing for the victims of war crimes," James Ross, the legal and policy director at Human Rights Watch, said.

"Real progress on justice demands an international investigation."

The report notes that under international law, an international inquiry can be imposed without a government's consent "when the state concerned lacks the capacity, political will, or both to undertake an independent, credible, and effective inquiry itself". 

But it says it is too early to tell whether the LLRC will prove as ineffective as the previous inquiry, and encouraged the government of Sri Lanka "to strive to act in accordance with best practices" in investigating the allegations.

After a decades-long military campaign, the Sri Lankan army defeated the LTTE, who were fighting to create an independent Tamil state in the north and the east of the island, in May 2009.

The UN has said that at least 7,000 Tamil civilians were killed in the final stages of conflict.