Concern has been expressed around any potential impact of the Government’s legacy bill on a fresh probe into the La Mon bomb attack.
Twelve people were killed and scores more injured when the Provisional IRA exploded a bomb at the hotel on the outskirts of Belfast in 1978.
The Police Ombudsman started a new investigation into the atrocity last year.
Victims group Ulster Human Rights Watch (UHRW) has expressed concern this probe could be impacted by the legacy bill.
It would also halt future civil cases and inquests linked to killings during the conflict.
The bill has been widely criticised by Northern Ireland’s political parties, the Irish Government and victims’ groups.
UHRW advocacy service manager, Axel Schmidt said the group has written to Prime Minister Rishi Sunak seeking assurances the Ombudsman investigation will be able to continue.
“This is a straightforward matter for relatives and survivors of La Mon: can the Ombudsman’s Office proceed with the investigation it started in 2022 and expects to have completed in April next year,” he said.
“The sole major obstacle that could jeopardise the completion of this investigation is the Northern Ireland Troubles (Legacy and Reconciliation) Bill, which may come into force in the near future.
“For this reason, taking into account the seriousness of this case and the length of time the victims have been waiting for this investigation to be carried out, I have asked that the Prime Minister urgently intervene so as to ensure that this investigation can be continued by the Police Ombudsman for Northern Ireland until its conclusion.
“Survivors and relatives will take great comfort if the Prime Minister agrees.
“If, on the other hand, he refuses the request, then those who are left with the traumatic injuries of that awful night will be denied access to the truth and feel left behind, abandoned and betrayed by their Government.
“It would be a shocking disregard of their suffering and resilience over many years if they were to fail to get this all-important assurance from the Prime Minister.”
A UK Government spokesperson said: “The UK Government is determined to deliver better outcomes for those most affected by the Troubles, while helping society to look forward.
“The Northern Ireland Troubles (Legacy & Reconciliation) Bill will establish an Independent Commission for Reconciliation and Information Recovery (ICRIR) to conduct reviews into Troubles-related deaths and serious injury, with the primary objective of providing information to families, and victims and survivors.
“It will have all the necessary powers to conduct criminal investigations as part of any review.
“The Government tabled a number of amendments during committee stage in the House of Lords that seek to address a number of key issues raised by stakeholders.
“We will continue to engage constructively with all interested parties, and to carefully consider how their concerns might be addressed as the Bill proceeds through Parliament.”