The Council of Europe has urged the British government to repeal immunity provisions in its controversial Legacy Act, saying it "risks breaching obligations under Article 2 of the European Convention to prosecute and punish serious grave breaches of human rights".
The international body, which oversees compliance with the European Convention on Human Rights, "strongly urged" the British government to consider rolling back on the prospect of conditional amnesties for people who provide information to a new commission.
It came as the organisers of a major legacy conference due to be addressed by former Chief Justice Declan Morgan faced calls to cancel the event.
Some of those who had initially been expected to take part are also understood to have withdrawn in recent days.
The Legacy: Reaching Beyond the Past conference, organised by the Law Society, is due to take place at the Hilton Hotel in Belfast on September 29.
The conference is open mainly to members of the legal profession.
It is due to take place days after the British government's controversial Legacy Bill passed into law.
Multiple legal challenges against the legislation have been lodged with the High Court in Belfast.
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It emerged on Friday that concerned relatives, victims and campaign groups, including Relatives for Justice, the Pat Finucane Centre and Justice for the Forgotten, are set to hold a picket outside the hotel venue during the conference next Friday.
The Time for Truth Campaign will also join the all-day protest.
It wrote to the Law Society on Friday urging it to cancel the conference.
Among those expected to participate are former Lord Chief Justice Declan Morgan, who was recently appointed chair of the Independent Commission for Reconciliation and Information Recovery (ICRIR).
The Irish News understands that some of those who had initially been expected to take part in the conference have withdrawn in recent days.
It is also understood that several legal firms involved in legacy and human rights work have indicated that they will not attend.
Alongside immunity provisions, the contentious legacy legislation, branded the 'Bill of Shame' by opponents, will end all inquests and civil cases.
The Northern Ireland Troubles (Legacy and Reconciliation) Act received royal assent earlier this week.
The recently established ICRIR will now oversee the handling of all conflict-related cases going forward.
Relatives of people killed during the Troubles who are opposed to the legislation say they will not co-operate with the new body.
Mark Thompson of Relatives for Justice said a picket line will be put in place outside the Hilton Hotel from early next Friday.
He said the legislation "is incapable of working in the interests of victims and delivering justice".
A spokesman for the Time for Truth Campaign said the new law "has created anxiety and distress among victims of the conflict who now see the shutters pulled down on their legal right to an investigation, inquest, and civil action".
"This bill has been rejected by all political parties on this island and has been the subject of sustained criticism from the international human rights community."
A spokesman for the NIO said the act contains "finely balanced choices for all".
"Now that the legislation has become law, the ICRIR will need time and space to establish itself," he said.
"The UK Government will be doing all it can to support the ICRIR in delivering effectively for victims and families."
The ICRIR and Law Society were contacted.
