AFP/Colombo

Sri Lanka promised Thursday to punish those found guilty of war crimes but stopped short of supporting an internationally backed probe, a day after a damning UN report on abuses committed during the island's conflict.

Foreign Minister Mangala Samaraweera said the government would work with the international community to ensure accountability and reconciliation following the island's separatist war, which ended in 2009.

But Samaraweera did not commit to the UN's key recommendation to allow international experts to assist its domestic investigation, saying more discussions were needed with stake holders.

He said the government would establish its own "credible, domestic mechanism" within 18 months to probe allegations in the UN report.

"We have a well crafted and a sober report," Samaraweera said. "It is now up to us to investigate and ensure justice is rolled out."

"Whoever is responsible, if proved, we will punish them without considering their rank or position," Samaraweera told reporters in Colombo. "By doing that we can protect the good name of the army."

Releasing the long-awaited report on Wednesday, UN rights chief Zeid Ra'ad Al Hussein said Sri Lanka needed international help to address the "horrific level of violations and abuses" during the decades-long war.

President Maithripala Sirisena came to power in January promising reconciliation between majority Sinhalese and minority Tamils and accountability for atrocities in the conflict, in which 100,000 people died before the Tamil Tigers were crushed. 

Colombo, which is planning a series of measures to achieve reconciliation including the creation of a truth commission, had been hoping to win the UN's backing for a domestic probe.

Sri Lanka's main Tamil party welcomed the UN report and urged Colombo to implement it.

In a statement, the Tamil National Alliance admitted there had been "unspeakable crimes committed in our name," but said the party was keen to support reconciliation.