Ulster Unionist leader David Trimble, Sinn Fein President Gerry Adams and the SDLP's leader John Hume will join Mr Blair and Mr Ahern in Downing Street next Thursday.

The announcement follows a meeting between Mr Blair and Mr Adams in Downing Street on Thursday.

The 45-minute meeting came on the same day the prime minister and Northern Ireland Secretary Mo Mowlam held talks at Number 10 with the province's smaller parties.

A Downing Street spokesman said Mr Blair and Mr Adams updated each other on progress, and that the prime minister made it clear that he would "continue to work to find a way through the current difficulties".

Gerry Adams met with Mr Blair for 45 minutes

A Sinn Fein spokesman said Mr Adams had used the meeting to urge Mr Blair to stick to the terms of the Good Friday Agreement.

At Stormont, meanwhile, inter-party talks between the Ulster Unionists, the SDLP and Sinn Fein were adjourned to next Tuesday following further "useful discussions".

The second day of the tripartite talks yielded no significant breakthrough, but the fact that they were scheduled to resume was being taken as a hopeful sign.

The Ulster Unionist Party was still insisting that the IRA must hand in weapons before the new Northern Ireland executive takes up its powers.

Sinn Fein has said decommissioning is not a precondition for devolution under the Good Friday Agreement.

Peace process 'in grave danger'

Gary McMichael: "The peace process is drifting"

Earlier, Ulster Democratic Party leader Gary McMichael told Mr Blair in London that the peace process was "in grave danger of falling apart".

Before going into Number 10 to see the prime minister, Mr McMichael, whose party has no seats in the assembly and is linked to the outlawed Ulster Freedom Fighters, said the peace talks were drifting following the collapse of the Hillsborough Declaration.

"If the executive were to be formed now in current conditions where Sinn Fein have made no attempt, absolutely no attempt, to find a middle ground, then we believe it will signal an end to unionist support for agreement," he said.