TD Gerry Adams has ignored mounting pressure over the Jean McConville murder and instead called for an international process to deal with the North's past.
Two deceased IRA members, Dolours Price and Brendan Hughes, claimed before their deaths that Mr Adams ordered the murder of Ms McConville, a Belfast mother-of-10, when he was a Provo commander.
And Justice Minister Alan Shatter claimed others will "ultimately judge" if the Louth TD is telling the truth.
He said: "I find the approach of Gerry Adams and Sinn Fein difficult to accept. There is an enormous credibility gap around Gerry Adams' approach to this."
Mr Adams has repeatedly denied the allegations about the McConville murder. And he said efforts to deal with the past have not made progress since the Good Friday Agreement.
He added: "Sinn Fein has proposed an independent international based process to deal with the past.
"None of the participants to the conflict can be responsible for creating such a process. The British Government has refused to agree on any mechanism that can deal with this issue and the Irish Government has made no real effort to establish a viable truth recovery process. This is not acceptable."
Fianna Fail TD Willie O'Dea backed calls for a special Dail debate on the murder claims.