Prime Minister Tony Blair: "Important to get extra momentum behind this process"

He admitted the talks were "at a difficult juncture" but said some forward movement had been made towards setting up the North-South cross border bodies, an integral part of the Good Friday Agreement.

The UK Prime Minister, Tony Blair, met all the main parties during talks to try to narrow the gap between nationalists and unionists over the shape of the new shadow executive for the Northern Ireland Assembly and cross-border bodies.

On Thursday Mr Blair will make history when he becomes the first British prime minister to address the Republic of Ireland's parliament, the Dail.

BBC Ireland Correspondent Denis Murray: The prime minister is acutely aware of the historic nature of the visit

He is expected to tell the Parliament that despite current difficulties the peace progress has gone too far to turn back now.

Mr Blair's visit will open a new chapter in Anglo-Irish relations as it is the first time a British prime minister has visited Ireland to discuss relations between the two countries rather than just Northern Ireland or European issues.

It is possible Mr Blair's visit could pave the way for a member of the Royal Family to follow in the future.

Mr Blair said earlier: "I believe we can make progress, I believe that the parties to the agreement want to make the agreement work."

And added: "I'm going to do everything I can to push it on and to keep the momentum going."

Gerry Adams: "Agreement stymied by unionists"

But Sinn Fein leader Gerry Adams added his voice to the growing concern around the peace process earlier in the day.

Emerging for a meeting with Mr Blair, he said: "No-one likes the word crisis, but this is a serious situation."

"Clearly the creditability of the agreement comes more and more into question as the drift continues.

"People are concerned that the promise of the Good Friday Agreement has been stymied by unreconstructed unionists."

Mr Adams was speaking after Northern Ireland's deputy first minister warned the agreement could fall apart within days unless decisions on the vital issues are taken.

Seamus Mallon: "Very afraid of inertia"

Seamus Mallon said he was "very afraid of inertia" and warned details of the shape of new Northern Ireland institutions must be agreed by the beginning of next week.

"If not, we will be in great danger of this process losing credibility," said Mr Mallon, also deputy leader of the nationalist SDLP.

Seamus Mallon: "Grave danger that the political process will lose credibility"

But Mr Adams insisted there was no reason why the institutions could not be sorted immediately.

David Trimble: "Some issues remain unresolved"

According to the Assembly's First Minister and Ulster Unionist leader David Trimble, all sides are understood to be close to agreeing arrangements for north-south institutions.

But there are still differences over the number of government departments, which should be set up in advance of next February's transfer of legislative powers from London to Belfast.