Time is running out for Northern Ireland to reach a final political settlement, the Taoiseach warned tonight.
Emerging from talks with British Prime Minister Mr Blair in Downing Street, Mr Ahern said the parties would have to resolve their differences soon.
He warned: "We can't sit around for ever."
"I really think it is time to come to an agreement... If not, this will drift way out and that would be a terrible mistake."
Mr Ahern was commenting after hour-long talks with Mr Blair on a formula to be put to the parties next week.
Both leaders are hoping to secure a significant gesture from the IRA which will persuade Mr Trimble's Ulster Unionists to go back into government with Sinn Féin.
Sources in Dublin and London believe a statement from the IRA declaring an end to all paramilitary activity such as recruiting, training, targeting and importing weapons as well as further disarmament moves would persuade unionists.
However Sinn Féin has insisted the context for achieving the removal of all armed groups is the full implementation of the Belfast Agreement by Mr Blair's government.
Sinn Fein president Gerry Adams today demanded further criminal justice reforms, more moves on policing, the implementation of commitments on human rights, equality and the Irish language.
It is believed the governments have also offered the prospect of British Army installations being dismantled and operations scaled down over a three year period.
However Mr Adams insisted republicans had still to see anything substantial. The West Belfast MP said: "The British government have not thus far come forward with the substance which matches what Mr Blair said last October.
"They haven't done it so far."
The Belfast Agreement can be saved with crucial peace process talks next week, SDLP leader Mr Mark Durkan said tonight.
However the Foyle MLA said he was less certain that the Agreement would be saved.
In his speech in Dublin, Mr Durkan again said people were losing faith with politicians.
Politicians, he said, needed to "fulfil the democratic will of the people" instead of arguing about what needed to be done.
"This will mean an end to all paramilitary violence and an end to all paramilitary organisations," the SDLP leader said.