The Taoiseach travels to Downing Street today for the opening of a fortnight of political talks which he says will cause "a big dilemma" for the North's political process if they end without agreement.
Mr Ahern and the British Prime Minister, Mr Tony Blair, will today meet leaders of the Ulster Unionist Party, Sinn Fein and the SDLP in further efforts to reach agreement on the four outstanding issues that are stalling the political process.
Speaking to reporters in Gothenburg at the weekend, Mr Ahern said the first issue - policing - "has not moved on a lot" in recent times. "We know where we are on policing and we know the views of the parties," he said.
The SDLP and the Government were ad idem on the issue and it was clear what was required, he added.
On the second issue, the stability of the political institutions, "David Trimble has the main call on that," he said. There could not be "stop-go" on the operation of the institutions.
On decommissioning, there had to be "a process and clear understandings of how it would be dealt with. If we don't get a clear position on that . . . we are unlikely to get the kind of movement that Sinn Fein and the SDLP want in the demilitarisation area."
The Ulster Unionists, the SDLP and Sinn Fein will hold separate discussions with the Taoiseach and Mr Blair today.
Sources said the UUP delegation would be adopting a particularly tough stance following the DUP's election successes. The leading anti-agreement MP, Mr Jeffrey Donaldson, who has been added to the team by Mr Trimble in an attempt to secure greater party unity, said: "I will be saying very firmly to the Prime Minister that he needs to take action over Sinn Fein's failure to deliver IRA decommissioning. I will also tell him there must be no more concessions to republicans on policing."
Sources said the talks are likely to continue in Belfast later this week under the chairmanship of the Northern Secretary, Dr John Reid, and the Minister for Foreign Affairs, Mr Cowen.
Meanwhile, sources close to Mr Donaldson have said he is unlikely to challenge Mr Trimble for the party leadership at the Ulster Unionist Council meeting on Saturday. It is not known whether another anti-agreement MP, the Rev Martin Smyth, will still stand against Mr Trimble.