The human rights watchdog issued a 69-page report slamming the work of the government's Lessons Learnt and Reconciliation Commission (LLRC) ahead of next week's meeting of the UN Human Rights Council, expected to  discuss Sri Lanka.

The report cited eyewitness testimony and information from aid workers suggesting that at least 10,000 civilians were killed in the final military offensive which crushed the separatist Tamil Tiger rebels in May 2009.

It accused the Sri Lankan army of shelling areas it knew to be densely populated by civilians, and also condemned the rebels for using non-combatants as human shields.

The report titled "When will they get justice?", said the LLRC, set up by the government, was "flawed at every level: in mandate, composition and practice".

Highlighting the number of ex-government officials on the commission, Amnesty said it had failed to investigate evidence of systematic violations, including illegal killings and enforced disappearances.

"The international community must not be deceived into viewing the LLRC as a credible replacement for an international inquiry -- this would allow war crimes and crimes against humanity to go unchallenged," said Amnesty's Asia-Pacific director, Sam Zarifi.

The defeat of the Liberation Tigers of Tamil Eelam (LTTE) ended nearly four decades of fighting which had claimed up to 100,000 lives.

The Sri Lankan government maintains that not a single   civilian was killed by its security forces.

However, an April report by a panel commissioned by the UN noted "credible allegations" of war crimes committed by both sides.

Colombo has managed to stave off censure at UN forums thanks to the support of close allies China and Russia, but a vote at the Human Rights Council cannot be blocked by veto-wielding powers.

Amnesty said that the LLRC was just the latest in a long line of failed domestic inquiries.

"Impunity has been the rule rather than the exception, now exacerbated by a post-conflict triumphalism that rejects all responsibility for abuses carried out by government forces," said Zarifi, who urged the international community to push for an independent investigation.

"Only then will the voices of victims really be heard," Zarifi said. "And only then can the process of post-conflict reconciliation begin to move forward."

Last month, Sri Lankan President Mahinda Rajapakse lifted a 28-year-old state of emergency which conferred sweeping powers of search and detention on the security forces.

But the government has since enacted new regulations granting similar powers under the Prevention of Terrorism Act. (AFP)