The BBC's Tom Coulter reports: "The deal he brokered is step by step falling into place"

The former US senator is to make his final statement on the progress of the peace talks at the end of the 11th week of the review.

He returned to Belfast on Wednesday night as dissension grew within the Ulster Unionist Party over the IRA statement on arms.

Northern Ireland Secretary: Peter Mandelson

Just before the review statement Northern Ireland Secretary Peter Mandelson praised the work of Mr Mitchell and thanked him for dedicating four years of his life to the peace process.

In a statement in Downing Street he added that the province's political parties have "a very great responsibility indeed for making sure that what has been achieved is taken forward".

Earlier, Ulster Unionist MPs issued a statement rejecting the IRA pledge to appoint an interlocutor to the International Body on Decommissioning once Sinn Fein ministers took their places in Northern Ireland's Executive.

Party leader David Trimble moved quickly to dissociate himself from the statement supported by six UUP MPs at Westminster.

Archbishop Robin Eames: "Look how far we have come"

Five of the party's House of Commons nine-strong team are understood to have authored the statement in which the IRA's pledge to appoint an interlocutor to deal with the International Commission on Decommissioning was dismissed as "totally inadequate".

'No certainty'

They included William Thompson, William Ross, Roy Beggs, Clifford Forsythe and Martin Smyth. The Lagan Valley MP Jeffrey Donaldson later issued a statement supporting the dissidents' stance.

"The IRA statement offers no certainty or clarity on decommissioning, no timetable for disarmament and no guarantee that it will actually happen.

"This deal effectively removes the lines between democracy and terrorism and we urge the wider party to stand by our manifesto pledges."

The statement was rejected almost immediately after its publication on Wednesday evening by the Ulster Unionist leader.

David Trimble: Moved quickly to counter dissidents' statement

"I wish to make it clear that I dissociate myself from a statement issued tonight in the name of the Ulster Unionist parliamentary party which received the endorsement of five members at the weekly meeting in Westminster," said Mr Trimble in his statement.

Earlier on Wednesday, Sinn Fein president Gerry Adams expressed confidence that any remaining obstacles in the Northern Ireland peace process can be overcome following the publication of the IRA statement at lunchtime on Wednesday.

But Mr Adams warned that success would depend on the parties and governments involved in the process maintaining a "cautious and measured approach".

He said the limits to which his party and its constituency had been stretched by the latest developments should not be underestimated by the British establishment and wider Unionist family.

He appealed directly to the British government to resist the temptation to over-hype the progress made since the beginning of the week and urged it to adopt an approach which was "sure-footed" and "calm".

Gerry Adams: "Obstacles can be overcome"

"Everyone in leadership needs to be mindful that peace-making is more important, is different from, more difficult than conventional politics or what usually passes for conventional politics.

"It means trying to put yourself in the shoes of your opponents, it means resisting the temptation to go for short term advantage, it involves resisting the urge to misrepresent, hype or to exaggerate," he said.

"As much as anything else, the success of the next phase may depend on everyone taking a measured and accurate approach in the period ahead."

Ulster Unionist negotiator Michael McGimpsey said the IRA statement could convince his party that republicans are serious about decommissioning.

'Enhances prospect of peace'

Mr McGimpsey said the way could now be open for the formation of an executive.

"There is a possibility that we could be in business.

"Business for us is achieving our party's twin objectives of decommissioning and devolution - crudely put 'no guns, no government'."

Irish Taoiseach, Bertie Ahern: "IRA statement is a positive development"

Irish prime minister Bertie Ahern described the statement as a positive development when taken in tandem with Tuesday's declaration by Sinn Fein.

He said the previous IRA statement was seen as a less than positive endorsement of the agreement arrived at Hillsborough in April and a lack of a statement July was a setback.

The IRA statement was also welcomed by Social Democratic and Labour Party (SDLP) leader John Hume who said it marked a "further advance towards the establishment of all the political institutions of the agreement and the process of decommissioning."