The Taoiseach and the British prime minister will host talks with Northern parties next week aimed at breaking the political impasse and restoring the Stormont institutions.
Mr Ahern and Mr Blair will co-chair bilateral meetings with the parties at Lancaster House in London on Friday but there will be no round-table session.
Spokesmen for both governments said the talks would assess progress made at the Belfast Agreement review, in Belfast, since February and at various meetings between the parties and government officials.
The governments want a renewed push for progress in September following what they hope will be another quiet summer on the streets of Northern Ireland.
Mr Blair and the Taoiseach agreed to convene the Lancaster House talks at a private meeting yesterday in Brussels, where they were attending the EU summit.
The European Council signalled its desire to see the PEACE II funding scheme for Northern Ireland extended by two years to 2006.
The decision to call talks came as a surprise following some downbeat assessments yesterday of the chances of progress in the short term.
The four main parties last night confirmed they would attend the talks. The Democratic Unionist Party, now the largest party in the North, viewed the talks as a stock-taking exercise but said a delegation would attend, just as they had taken part in the review and in discussions with both governments so far.
A spokesman for the Ulster Unionist Party claimed the initiative would be more productive than the review, which the party is boycotting pending an end to paramilitary activity.
Sinn Féin said agreement on all outstanding difficulties would not be reached in the few days before Lancaster House. However, a spokesman said that an agreement could be reached in London on a means to resolve all unresolved matters over the next few months which, in turn, could bring about a restoration of the Stormont institutions before the end of the year.
The Sinn Féin president, Mr Gerry Adams, is to brief the party's ardchomhairle on the talks today and is expected to refer to them in his Wolfe Tone commemoration address at Bodenstown tomorrow.
The SDLP welcomed the decision of the two premiers to commit time to Northern Ireland. Dr Alasdair McDonnell, the deputy leader, said: "I welcome the fact that the two prime ministers have re-engaged and found time to put Northern Ireland back at the top of the agenda."
The talks have presented serious scheduling difficulties for the Government. Mr Ahern flies to the Far East for the EU-Japan summit on Monday and returns to Ireland late on Wednesday.
The London talks will be concluded by early Friday afternoon in time for the Taoiseach to return to Shannon to welcome President George W. Bush.