The British Prime Minister Tony Blair has said unionists must be prepared to go into government with Sinn Féin if republican paramilitary activity ceases.
The Taoiseach Mr Ahern and Mr Blair are to meet on Friday and are expected to assess the prospects for restoring devolution.
Devolution was suspended by the British government in October 2002, when the power-sharing executive threatened to collapse amid unionist claims about IRA activity.
The UUP's David Burnside today urged Mr Blair to tell the republican leadership its "time had run out" and they were delaying the establishment of Stormont.
Mr Blair said he had consistently made clear there was no way the institutions could function again without a total cessation of all paramilitary activity.
"That has been made clear throughout and I can assure you that I will be making exactly the same points again," he pledged.
But it was important to try to reach agreement backed by all parties. "That has to be on a clear, shared democratic understanding."
Mr Blair continued: "I can assure you that there is no way we will be trying to force people into an executive and shared power with people unless they are prepared to give up their paramilitary activity completely."
He stressed: "If the IRA do definitely and clearly cease paramilitary activity and give it up, so that that campaign of violence in all its aspects becomes a thing of the past, I hope that the DUP and the UUP will be prepared to go into Government with them.
"In my view the challenge is for the IRA to give up violence completely but then the challenge is for all the parties to come together and make the executive and all the institutions work."
PA