Amnesty International said the victims of Troubles violence have been let down by an inadequate patchwork of investigations and a lack of political will to heal divisions.
Director for Europe and Central Asia, John Dalhuisen said: "There's a cruel irony in the fact that Northern Ireland is held up as a success story when many victims' families actually consider their treatment a failure."
The publication of the 78-page document comes 15 years on from the Good Friday Agreement and one week ahead of a major new round of talks on the past.
American diplomat Dr Richard Haass will chair all-party discussions hoped at resolving contentious issues such as flags, parades and the legacy of the Troubles.
Amnesty said victims and their families had been let down by the Historical Enquiries Team, which has been criticised over its handling of cases involving the military.
It further questions the remit of the Police Ombudsman and various coroners' inquests.
Mr Dalhuisen continued: "Over the last decade a patchwork of measures, including isolated investigations, have failed to establish the full truth about the violations and abuses of the past and left many victims waiting for justice.
The UK government and all political parties in Northern Ireland need to grasp the nettle now and agree a new approach which is capable of dealing fully with the past.
John Dalhuisen, Amnesty International
The Troubles claimed more than 3,600 lives, with the violence hitting communities across Ireland, in Britain and, on occasions overseas. More than 40,000 were injured during the conflict.
The report was published on the same day when the NI Secretary of State Theresa Villiers said there would be no public inquiry into the Omagh bombing.
Relatives of those killed have said they will seek a judicial review.
Elsewhere a daughter of a victim in the McGurk's bar bombing in Belfast has been granted permission by the High Court to challenge the non-disclosure of a report into the massacre.
Sinn Féin MLA Mitchel McLaughlin said the party's position remains that an "independent, international truth recovery body" was the mechanism needed to deal with the past.
"The foundation of such a process cannot have the British government as so called arbiters - they were a party to the conflict and as such continue be involved in coverups while refusing to deal adequately with issues such as collusion and shoot to kill," he said.
"Sinn Féin will be presenting these comments and our perspective on how to deal with the past at the Haass talks."
But Unionist representatives have criticised Amnesty International's "discrediting" police and security forces.
This latest report once again appears to fall into the usual pattern of placing a focus almost entirely on the state to be made accountable for the actions of police officers and the security forces.
Jeffrey Donaldson, DUP MP
Ulster Unionist Justice spokesperson Tom Elliott claimed the report had been compiled with "a one-sided approach".
"The authors even go so far as to claim there should be a single mechanism for dealing with the past, while at the same time calling for public inquiries into the Finucane killing and the Omagh atrocity, which is obviously putting these outside the single process. This is a great example of double standards," he commented.
Mr Elliott accused the organisation of using the report to push their "pet project" for a Northern Ireland Bill of Rights.
Meanwhile DUP Lagan Valley MP Jeffrey Donaldson argued the report's recommendations for addressing the past were lacking.
"Whilst issues such as compelling retired police officers to submit to interview are the subject of specific recommendations there are simply vague aspirations that somehow those involved in terrorist gangs could be persuaded to admit their role," he said.
"Indeed the only real area of interest to Amnesty when it comes to paramilitary organisation is in relation to allegations of collusion with forces of the state."
Mr Donaldson said the upcoming cross-party process "is far more likely to deliver progress".
SDLP West Belfast MLA Alex Attwood, who will represent his party along with Joe Byrne at the upcoming talks, said the report highlights a number of key challenges to resolving issues around the past.
"The Haass talks must live up to these truths," he stated.
"The great risk and clear evidence is that there will be those inside the Haass talks who will resist truth and accountability, protecting the vested interests of state organisations and terror groups.
"Indeed there are those outside the talks who will also resist the truth, such as the British Government, who today refused to instigate a public inquiry into the circumstances around the Omagh bombing.
"There cannot be truth if elements in the police, army, and security service or those who controlled and directed the terror groups protect themselves and their own interests. That issue needs to be confronted. The needs of victims must prevail."