International human rights groups have refused to appear before a Sri Lankan inquiry into the end of the country's civil war, saying the procedure is flawed and lacks credibility.
They say the Lessons Learnt and Reconciliation Commission (LLRC) does not meet international standards.
But the commission, appointed by President Mahinda Rajapaksa, says it is a credible attempt for reconciliation.
Correspondents say the panel has no real mandate to investigate the truth.
The International Crisis Group (ICG), Human Rights Watch (HRW), and Amnesty International (AI) have all refused to appear.
They argue that the commission is flawed because its members were appointed by the government, has no real mandate to investigate war crimes in the last stages of the conflict, lacks any mechanism to protect witnesses and falls short of minimum international standards of a commission of inquiry.
They all said they would welcome an opportunity to appear before a genuine effort on reconciliation and accountability
"Accountability for war crimes in Sri Lanka demands an independent international investigation," said Kenneth Roth, of Human Rights Watch.
The group said the president's appointment of the LLRC was "an apparent attempt to deflect calls," for an international investigation.
President Mahinda Rajapaksa appointed the commission in May primarily to investigate why a Norway-brokered cease-fire between the government and the Tamil rebels signed in 2002 collapsed.
Both the Sri Lankan government troops and the Tamil Tigers are accused of war crimes during the last stages of war.
The government has denied committing any such offences.
Amnesty International's Madhu Malhotra said the group was concerned about the lack of provisions for witness protection.
And "former officials who have publicly defended the Sri Lankan government against allegations of war crimes serve on the commission," she said.
The UN secretary general has appointed a panel to advise him on accountability issues on Sri Lanka. Rejecting the panel, the government said it would not grant visas to UN panel members to visit Sri Lanka.
