The UN High Commissioner for Human Rights has said the UK Government's Northern Ireland 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 to be incompatible with the UK's international human rights obligations.
The Northern Ireland Troubles (Legacy and Reconciliation) 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.
The proposed law changes are opposed by all Stormont's main parties and the Irish Government, as well as victims' groups in the region, which have denounced it as an "amnesty" for killers.
This week, the Government moved to change proposals for the truth recovery body to be able to conduct criminal investigations "where it judges that to be appropriate".
In a statement on Thursday, Mr Turk said: "I recognise that addressing the legacy of the Troubles from the 1960s to the 1990s is 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."
The High Commissioner previously wrote to the 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.
Mr Turk said: "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."
"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."
The Bill is scheduled to proceed in the House of Lords next week.
The High Commissioner also said that announcing the proposed amendments to the Bill one week before the House of Lords committee stage gives "insufficient time" for those interested to "scrutinise the amendments and participate meaningfully in this hugely significant legislative process."
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. Their rights must be placed at the heart of all attempts to address the legacy of the Troubles.
"I urge the UK to reconsider its approach and engage in further meaningful and inclusive consultations on how best to advance a human rights-centred way to address the legacy of the Troubles."
Grainne Teggart, deputy director for Northern Ireland at Amnesty International UK, welcomed the comments.
"This is a significant, timely and welcome call from the UN Human Rights chief which the UK Government must not ignore," she said.
"The Government must recognise and understand the scale of international concern about this Bill, which betrays victims of the Troubles and also diminishes any claims by the Government that they stand for human rights.
"In light of this latest intervention, we call again for the UK Government to pause the legislative process, drop the Bill and meaningfully commit to a way forward which puts victims at its centre."
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