Review chairman, former US Senator George Mitchell, met Peter Mandelson in London after political talks involving all the pro-Agreement parties broke up without any sign of a breakthrough.

It is thought the senator gave Mr Mandelson details of what occurred during two days of intense and private negotiations in London.

BBC NI Political Editor Stephen Grimason: "More crucial meetings next week"

The crucial talks yielded little agreement on the two main issues - decommissioning and the setting up up a Northern Ireland Assembly executive.

But BBC Political Editor Stephen Grimason said: "My antennae are twitching here, that there's maybe something more about all of this, than is being told to us. That's not surprising, given these are very private talks."

After the talks ended, Social Democratic and Labour Party (SDLP) deputy leader Seamus Mallon said important discussions would take place next week.

He said it was "impossible to quantify" what progress, if any, had been made.

"I would say that the atmosphere was good, that there was engagement, that there was an intensity about the meetings, that I think was satisfactory," he said.

As discussions concluded, Sinn Fein's Gerry Kelly said there had been a "more conducive atmosphere".

Gerry Kelly of Sinn Fein: "We are committed to the Good Friday Agreement"

"In negotiations everything is give and take, but from our point of view, we would argue there's been a bit too much take over the last 18 months, without give on the institutions which we're agreed on," he said.

"If the review is to finish next week, we need to be at least hopeful that we are here because we are absolutely committed to the Good Friday Agreement and we want it to work. Our push and our hope is to sort that out."

Senator Mitchell moved the talks to London on Tuesday. Round table talks followed separate discussions on Thursday morning which involved the Ulster Unionists, Sinn Fein and the SDLP.

The final meeting at Lancaster House was between the Ulster Unionists and Sinn Fein.

Sinn Fein leader Gerry Adams said early on Thursday that the atmosphere between the parties had improved.

"We are back here this morning for a series of bilaterals and trilaterals and multilaterals with the other parties. And we will, through this review, persevere in trying to have established the institutions which should have been put in place," he said.

Ulster Unionist leader David Trimble also said he was still committed to breaking the deadlock.

"This process will not fail through any want of effort on our part.

"But it has been the case, ever since we were ready for devolution in March, that we are ready to do our bit, and we have been delayed for six months because others are not yet ready to do theirs," he said.

It is the first time Mr Mitchell has taken the parties away from Stormont in Belfast since the review began last month.

The political impasse developed after the Ulster Unionists refused to sit in government with Sinn Fein until the IRA began to decommission its weapons.

Sinn Fein says decommissioning is not a precondition in the Agreement.

Meanwhile the Democratic Unionist Party (DUP) met with other anti-Agreement unionists at Stormont in Belfast on Thursday.