Unionists are demanding that Sinn Féin president Mr Gerry Adams be immediately arrested and questioned about the 1978 La Mon bombing in which 12 people died.
It follows a statement in the House of Commons by the DUP MP, Ms Iris Robinson, that Mr Adams sanctioned and approved the attack on the hotel on the outskirts of Belfast. The Sinn Féin president has denied the allegations.
Ulster Unionist MP Mr Jeffrey Donaldson said: "Sinn Féin is constantly demanding public inquiries into all kinds of things. It is now time for Gerry Adams and the IRA to come clean about their past actions. We have a right to the truth."
Speaking under parliamentary privilege on Thursday night, Ms Robinson said: "The police are certain this attack was sanctioned and approved by Gerard Adams, who was then in command of those who are known to have carried it out. The extent of his involvement in the planning and direction of the attack also needs to be probed."
Ms Robinson was speaking ahead of the 25th anniversary of the explosion on Monday. She said the bombing, in which the victims were burned to death, "defied human understanding".
Those who died had been attending the annual dinner dance of the Irish collie club. Ms Robinson said the PSNI was keeping the file open on the explosion but those responsible were not being actively pursued.
Calling for the families to be told the truth about what happened, she said: "There should be no cover-ups and no-one should be above the law. She accused the British government of putting in government people who carried out such atrocities.
"The distinct possibility is that a candidate for one of the top government posts after the next election will be the man who was arrested by the police during their investigation into this bombing and who is known to have control over the team responsible for this outrage and carnage."
Her demand for an independent inquiry into the atrocity was rejected by Northern Ireland Office minister, Mr Des Browne.
Mr Adams denied any part in the bombing. He said Ms Robinson's comments were made to deflect attention away from developments in the Stevens inquiry into collusion between the security forces and loyalist paramilitaries.