Senator Martin Mansergh has urged the IRA "not to do anything foolish" to wreck progress in the Northern Ireland peace process following two statements from the organisation.
Mr Mansergh, who has been Northern adviser to three taoisigh, said he felt sorry about the current crisis but excluding Sinn Féin from power-sharing talks would be disastrous.
Mr Mansergh told a student debate in Dublin's Trinity College "with their statement, the IRA seem to be angry and frustrated.
"But I would appeal to the republican movement not to do anything foolish. Not to damage anything that has been achieved by political leaders, some of whom are in Sinn Féin ."
Mr Mansergh was speaking after a second statement last night from the IRA in less than 24 hours warned the British and Irish governments not to "underestimate the seriousness" of current difficulties in the peace process.
The senator said he trusted the Taoiseach, Mr Ahern, when he claimed that Sinn Féin leaders had prior knowledge of December's £2.65 million sterling Northern Bank robbery. He said: "He is extremely careful. He doesn't say things lightly without having a lot of information."
Mr Mansergh said the record heist had brought trust in the peace process to an absolute nadir, and had a more destabilising effect than the bombing of Canary Wharf.
Democratic Unionist MEP Mr Jim Allister told the debate that it was time to move on without Sinn Féin and to have a "coalition of willing democrats".
He said: "You cannot have a mandate to play politics by day and play with terror by night." He insisted that the IRA had carried out the Northern Bank robbery and had been planning to do so for months.
Sinn Féin MEP Ms Mary Lou McDonald accused the Government of having a "cavalier and flippant attitude towards the very deep crisis" in the peace process.
She described Mr Ahern's claims of Sinn Féin knowledge of the Northern Bank crime as "wild and baseless", and claimed that he knew his comments would have "massively destabilising consequences".
PA