Sinn Féin vice-president Michelle O'Neill has described Operation Achille as a "devastating indictment of collusion between the British state and loyalist paramilitaries".
The former Deputy First Minister was speaking after Police Ombudsman Marie Anderson found there was "collusive behaviour" by police in the murder of 11 Catholics between 1990 - 1998.
“This report is a devastating indictment of collusion between the British state and loyalist paramilitaries," Ms O'Neill said.
“This is why the British government wants an amnesty for its state forces, intelligence services and the agents who killed for them.
"It is why victims, families, political parties and human rights groups continue to vigorously oppose these plans."
SDLP Policing Board member Dolores Kelly said the "report is a damning indictment of the RUC handling of loyalist paramilitary murders in south Belfast".
“Any one of the ombudsman findings would be damning," she said.
"But together they paint a disturbing pattern of police behaviours and investigations at the time.
"The same failings identified in this report were identified in the report into Operation Greenwich last month. It is becoming increasingly clear that these were not standalone issues with individual investigations."
Aontú deputy leader Denise Mullen also voiced concern about the contents of the report.
Her father Denis Mullen was shot dead by the Glenanne Gang, which included members of eh UDR, RUC and UVF, in September 1975 at their family home near Moy.
"The need for an All-Ireland inquiry into the death toll of British collusion cannot be denied any longer," she said.
"County by county, report after report, the full extent of British state-sponsored violence is becoming known.
"In the ‘Murder Triangle’ between Armagh and Tyrone, a British government-sponsored death squad made up of loyalist terrorists, members of the British Military in Ireland and RUC officers, murdered over 120 innocents across the north of Ireland."
Alliance Party deputy leader and north Down MP Stephen Farry said it was "notable the Ombudsman has once again identified collusive behaviours".
“This Ombudsman’s report delivers a number of incredibly disturbing findings regarding a series of failings by the RUC in terms of the management of agents and deficiencies of investigations,” he said.
“Today’s report will bring a range of mixed emotions for the families, from relief a comprehensive report has been published, or renewed trauma over the deaths of loved ones and thoughts whether deaths were avoidable."
DUP Policing Board member Trevor Clarke said:‘‘This is the latest in a growing list of reports by the Ombudsman which alleges collusive behaviour against police officers during the Troubles despite the fact that no such criminal offence actually exists.
"Tellingly the report makes no recommendations in terms of criminal proceedings and accepts that the RUC has no prior knowledge of the attacks."
