The Irish and British governments have said a way must be found through the impasse in the peace process in advance of the June elections.
Both the Taoiseach, Mr Ahern, and Mr Tony Blair warned of the dangers of political drift and the tendency for vacuums to be filled by what a British spokesman called "dangerous forces".
Mr Ahern said: "If we leave this to drift, it creates a vacuum. The present vacuum is not a satisfactory situation and it cannot be allowed to continue indefinitely."
They were speaking after a series of trilateral meetings with the Northern parties at Hillsborough Castle, Co Down.
There was also a side meeting between Sinn Féin and the Government during which Mr Gerry Adams sought assurances that no attempt to "criminalise" his party was being made.
The meetings, hosted by the two governments, involved the Democratic Unionists for the first time since the signing of the Belfast Agreement in April 1998.
Mr Blair, on his 33rd visit concerning the peace process, committed the two governments to further contacts with the parties as part of a concerted effort to revitalise the political process before June elections on both sides of the Irish Sea and the marching season on the North.
Speaking at a joint press conference with Mr Ahern, he said the issues were clear and had been clear for some time.
"On the one hand we need an end completely, totally and definitively to paramilitary activity, and on the other hand there has to be a willingness to share power across the political parties," he said.
Participants in the process had to adhere to democratic principles and there had to be "complete respect" for the mandate of the parties involved.
Mr Ahern said the Prime Minister's comments were in keeping with their objective, set out at Farmleigh earlier this month, to "fast-track" political efforts to restore the North's political institutions.
He said that if paramilitarism ended and commitments to share power and work the institutions were made then "we can make tremendous progress".
Despite continuing rumour to the contrary, and the express fears of Sinn Féin, Mr Blair said the governments did not wish to exclude any party from the political process.
"What we're looking for is a clear indication that paramilitary activity will cease completely so that everyone can be sure of moving forward on a democratic path," he said.
However, it was clear from remarks made by the delegations leaving Hillsborough Castle that deep divisions remain.
The Rev Ian Paisley, using language striking in its similarity to that used by Mr Blair in his "acts of completion speech" in Belfast in October 2002, said an end to violence had to be unambiguous.
The SDLP said the two governments should implement what they could of the agreement while current problems were addressed.
One talks insider from the party told The Irish Times that progress could not be put permanently on hold pending movement from paramilitaries.
The Alliance party criticised the two governments, accusing them of a lack of focus. Mr David Ford said that, rather than kick-starting the political process, the two premiers were just kicking ideas around.
Mr David Trimble, who faces a leadership vote at his party's a.g.m. on Saturday, said he expected a report in the near future from the Independent Monitoring Commission concerning the alleged attempted abduction of Mr Bobby Tohill by the IRA.