On the eve of a crucial meeting with the Sinn Fein President Mr Gerry Adams, the Taoiseach, Mr Ahern has called for all private armies to retire, and warned the time for "polite fictions" was over.
He said time was running out and the Belfast Agreement must not be allowed to languish and die.
"It is time for all Republicans to embrace the constitutional principles of the Agreement and for private armies to retire," he said.
"Everybody has continued to talk about the peace process but we're not following that up with the necessary actions."
In a speech apparently directed at Sinn Fein, Mr Ahern said the British and Irish governments wanted to move forward but the Agreement should not just be used as a talking point.
"Some have garnered and borrowed votes on the promise of the peace process," he said. "But the period for maintaining polite fictions and Chinese walls has expired. It's time to be honest. We can't be misleading people." Mr Ahern, speaking at the annual Fianna Fail commemoration ceremony in Dublin, said the time for talking was running out.
"We really need to see momentum achieved," he said. "I worry that we have lost so much time, so many months. The blame game is a hopeless game.
"To make progress everyone has to give and take but time is of the essence. The political parties need to get on, stop the rhetoric and get on with it." He made reference to the founders of the Republic, Padraic Pearse and James Connolly, paying tribute to their role in establishing a free Ireland.
"All of us appreciate the progress that has been made, and the contribution made by courageous political leadership in bringing us this far," he said.
"We must not baulk at the last fence. The dream of Pearse and Connolly can only be realised in time through full implementation of the Good Friday Agreement, provided we do not allow the Agreement to languish and die.
"Democratic politics and institutions cannot work with integrity alongside continuing illegal paramilitary activity. Public confidence must be restored."
The Taoiseach is due to meet Mr Adams in Dublin tomorrow.