Prime Minister Tony Blair and Irish Taoiseach Bertie Ahern will meet the Ulster Unionists, the SDLP and Sinn Fein on Monday as part of a week of talks in London, Belfast and Dublin.

The move follows the rejection by some of the main parties of the Hillsborough declaration, which attempted to provide a way forward on the decommissioning of paramilitary arms.

The declaration was set out by Mr Blair and Mr Ahern two weeks ago, but has now been rejected by Sinn Fein and the Progressive Unionists, which have links to the IRA and UVF paramilitaries respectively.

It has also been rejected by the Women's Coalition.

The BBC's Denis Murray: The two prime ministers are starting again

Northern Ireland's First Minister David Trimble, who as Ulster Unionist leader refuses to sit in an executive with Sinn Fein before decommissioning begins, welcomed multilateral talks.

But the key problem remained Sinn Fein's refusal to accept the obligation of the IRA to begin this process, he said.

"The question now for Sinn Fein is: is it prepared to implement all of the [Good Friday] Agreement, or is it moving to a position of repudiating the agreement?"

Democratic Unionist Party leader Ian Paisley said he believed Mr Trimble was prepared to back down and do a deal over decommissioning.

Mr Paisley said Mr Trimble's statement that he did not believe republican violence would ever be as bad as in the past were "the words of a man prepared to do a deal".

Sinn Fein question commitment

Sinn Fein President Gerry Adams insists the Hillsborough declaration amounts to an attempt to rewrite the Good Friday Agreement.

While the agreement, signed more than a year ago, makes no direct link between decommissioning and the establishment of the Northern Ireland Assembly executive, the declaration proposes a day of reconciliation, including arms disposal, within a month of ministers taking up their seats.

Gerry Adams: Rejects declaration

He has said that move follows pressure from Mr Trimble and has gone from "the common ground of the Good Friday Agreement, shared by all the pro-agreement parties last April, to the much narrower ground occupied by the Ulster Unionist Party".

His comments reflect Sinn Fein's frustration at Mr Trimble's refusal to allow it to take up its two ministerial posts in the province's executive until the IRA begins to dispose of its weapons.

Speaking on Friday, Sinn Fein Chairman Mitchel McLaughlin highlighted the "enormous anger and frustration" among nationalists and republicans at the developing crisis in the Northern Ireland peace process.

Mr McLaughlin said the only way out of the crisis was for the UK and Irish governments to take the lead and focus on what was required in peace process negotiations.

He said: "We are getting reports from right across the country of a very considerable amount of frustration at this attempt to rewrite the agreement.