The UN High Commissioner for Human Rights has said the British government's legacy bill must adequately ensure respect for the rights of victims, survivors and their families.
Volker Turk said the draft legislation as it stands appears incompatible with the UK's international human rights obligations.
The bill would provide immunity for people accused of Troubles offences as long as they co-operate with a new truth recovery body, and would also halt future civil cases and inquests linked to killings during the conflict.
Mr Turk said he recognised that addressing the legacy of the Troubles was a "hugely complex and sensitive matter".
"But the draft legislation as it stands appears to be incompatible with the UK's international human rights obligations," he said.
The high commissioner previously wrote to the British government over the proposed conditional immunity from investigation and prosecution for those accused of having committed serious human rights violations and other international crimes, other than sexual offences.
"Introducing conditional immunity in this manner would likely be at variance with the UK's obligations under international human rights law to investigate and, where appropriate, prosecute and punish those found responsible for serious human rights violations," he said.
"Concerns remain that the Bill would obstruct the rights of victims, survivors and their families to effective judicial remedy and reparations, including by prohibiting most criminal prosecutions and civil actions for Troubles-related offences."
Mr Turk said "insufficient time" had been provided to meaningfully scrutinise proposed amendments to the bill one week before the House of Lords committee stage.
Mr Turk added: "Respect for rights of victims, survivors, and their families to truth, justice, reparation and guarantees of non-recurrence is essential for reconciliation," he said.
"Their rights must be placed at the heart of all attempts to address the legacy of the Troubles."
Amnesty International UK's Gráinne Teggart described the high commissioner's intervention as "significant, timely and welcome".
