The United Nations on Wednesday detailed horrific abuses committed in Sri Lanka's civil war, including the disappearance of tens of thousands of people, and said the country needed international help to probe war crimes and enable reconciliation.
"A purely domestic court procedure will simply not succeed in overcoming the widespread and justifiable suspicions fuelled by decades of violations, malpractice and broken promises," UN rights chief Zeid Ra'ad Al Hussein told reporters in Geneva.
The country, he said, needed international assistance to address the "horrific level of violations and abuses" during and following Sri Lanka's 26-year civil war, revealed in a long-awaited report.
The report identified patterns of grave violations "strongly indicating that war crimes and crimes against humanity" had been committed by both sides.
Among other abuses, it found that tens of thousands of Sri Lankans remained missing after decades of conflict, suggesting enforced disappearances had been part of a systematic policy.
Sri Lanka's new unity government has promised dramatic reforms to achieve accountability for alleged atrocities during the war with the Tamil Tiger guerrillas, which ended in 2009 and killed at least 100,000 people.
The government, which is planning various measures to ensure reconciliation including the creation of a truth commission, had been hoping to win UN backing for a domestic probe.
But Wednesday's report concluded that "Sri Lanka's criminal justice system is not yet ready or equipped" to conduct an independent and credible investigation.
Instead, it urged the country to establish a "hybrid special court", including international judges, prosecutors, lawyers and investigators, to probe war-related abuses.
Zeid pointed out that a range of previous domestic investigations "were almost designed to fail".
He warned that "years of denials and cover-ups, ... stalled investigations and reprisals against the family members of victims" had taken their toll.
"The levels of mistrust in state authorities and institutions by broad segments of Sri Lankan society should not be underestimated," he said.
The seven investigators behind the report were not allowed into Sri Lanka but based their findings on interviews with victims and witnesses, video footage, photos, satellite images and other sources.
The report had initially been scheduled to be published in March, but Zeid had recommended it be delayed for six months to give the country's new government a chance to co-operate with investigators.
Sri Lankan President Maithripala Sirisena came to power in January promising reconciliation and accountability for alleged atrocities committed by troops under the command of then-president Mahinda Rajapakse.
During his decade in power, Rajapakse resisted Western pressure to investigate allegations that up to 40,000 ethnic Tamil civilians were killed by his troops in the final months of the conflict in 2009.
Zeid hailed the dramatic change of tone among Sri Lanka's leadership, saying it offered "grounds for hope," but warned that breakthroughs had been seen before in the country only to later stall.
Wednesday's report, which looked specifically at the period between 2002 and 2011, described widespread illegal killings by both sides and a deliberate policy by Sri Lankan security forces to use rape and sexual violence as torture against both women and men.
It found that children were often abducted by the separatists - from homes, schools, temples and checkpoints - and sent to the front lines as soldiers, while a group linked to the government had also recruited children.
Zeid warned that without deep reckoning with its past the country risked falling back into conflict.
A major remaining problem identified by the report was the lack of any reliable system for protecting victims and witnesses, while the culture that had allowed police and security services to act with "near total impunity" remained deeply entrenched.
It urged a "fully-fledged vetting process to remove from office security forces personnel and public officials suspected of involvement in human rights violations".
The report also called for Sri Lanka to invite the UN rights agency to establish an office in the country to monitor the situation.