Sri Lanka will conduct an investigation into allegations its troops committed war crimes during a conflict with Tamil separatists, it said Friday, a month before the UN Human Rights Council is due to discuss the island's rights record.

At least 100,000 people were killed in the decades-long civil war, and there were allegations that 40,000 Tamil civilians were killed in the final onslaught. The government denies the toll.

President Gotabaya Rajapaksa, who was defence chief when the rebels were crushed in 2009, named a commission of enquiry Friday to look into investigations held by previous governments.

The panel was given six months to look into allegations of "human rights violations, serious violations of international humanitarian law," his office said.

It would also be tasked with investigating previous "inconclusive investigations" instigated by Colombo following international pressure.

"Sri Lanka has a long history of Commissions of Inquiry that have repeatedly failed to deliver justice and reconciliation for victims of human rights violations," rights watchdog Amnesty International tweeted following the announcement.

The group urged the UNHRC to initiate a new process against Sri Lanka to ensure justice for victims of the war.

A commission appointed by the government in 2011 found there were credible allegations against government forces and called for a war crime investigation. This has never been started.

After coming to power, Rajapaksa announced that he would not follow a 2015 UNHRC resolution calling for accountability over alleged excesses by Sri Lankan troops at the climax of the 1972-2009 conflict.

Rajapaksa threatened in May last year to withdraw from the UNHRC if the body pursued war crimes allegations against his troops.

However, on Friday, his office said although Sri Lanka withdrew from the UNHRC resolution of 2015, it was ready to make "institutional reforms" to ensure justice and reconciliation.

aj/tw/rma