The Fine Gael leader Mr Enda Kenny has said that releasing the killers of Det Garda Jerry McCabe will "completely undermine the integrity and authority" of the office of Taoiseach.
Speaking in Navan at a party selection convention for the forthcoming by-election in Meath, Mr Kenny said the release of the killers would "prove categorically" that the Government is "incapable of distinguishing between right and wrong and of upholding Ireland's rule of law".
And he said Fine Gael in government would not release the killers.
He said the four men convicted of the killing were not 'freedom fighters' but "thugs and bank robbers" who had killed the garda "in cold blood".
"They were disowned by the Republican movement at the time and their release is, and never was, part of the Good Friday Agreement, a fact made clear before the Irish people voted to approve the Agreement in 1998," Mr Kenny added.
"Secondly, I believe it is the duty of any Government to stand by the institutions of the State. Therefore, the army council of the IRA should have no say in the rule of law and of justice in this country, never mind be its sole and final arbiter and at such a critical juncture in our island's painful history."
Mr Kenny said he believed a solemn commitment given by the Taoiseach and the Minister for Justice on behalf of the Irish Government and the Irish people should not be "overturned by the IRA army council".
"How else can the Minister for Justice look any Garda recruit in the eye at a passing out parade in Templemore and say 'this Government will stand by you as you put your life on the line for us'?"
The Fine Gael leader said he fully appreciated the critical stage of the negotiations on the peace process, but that the Taoiseach should never have allowed this matter to be part of the final agenda.