US Senator George Mitchell said the enormous contribution and leadership of the Taoiseach and the former British Prime Minister was "beyond any doubt and dispute".

"They came to Belfast at a critical juncture. They didn't just supervise, they conducted the negotiations. Line by line, word by word, they put together the agreement that led to the events that now exist in Northern Ireland," he said.

Senator Mitchell was speaking at an event in Dublin Castle to mark the 10th anniversary of the Good Friday Agreement.

Mr Ahern and Mr Blair were guests of honour at a dinner organised by the Turn the Tide of Suicide (the 3Ts charity).

Senator Mitchell said many people collaborated and contributed to making peace.

"But I can say with absolute certainty, without the personal effort and leadership provided by Tony Blair and Bertie Ahern, there would not have been a Good Friday Agreement," he added.

"Certainly there would not have been an agreement in the form that eventually was reached and the events of the past 10 years would have been very much different."

Mr Ahern paid tribute to Mr Blair saying it was entirely fitting he be honoured.

The Taoiseach said Britain is a big country with a lot of problems but "Tony gave so much of his time".

"We owe him a huge debt of gratitude for the time and commitment he gave," he said.

Mr Blair said there were times he thought the peace process "wasn't really going to work out".

"You know, when we look back over the 10 years, I think it's easy right at this moment to forget that at many points in time, the whole thing hung in the balance. Indeed, occasionally, I thought it wasn't really going to work out, but it did," he added.

Mr Blair said he hadn't offered any advice to Mr Ahern on what he should do after he steps down as Taoiseach.

"I don't presume I would offer the Taoiseach any advice," he said.

Bob Geldof, who has reportedly offered the Taoiseach a role in Third World development, was also at last night's gathering.

Pointing out that May 6 is his birthday, Mr Blair said the pair could go to a Manchester United versus Newcastle United match together -- albeit they would be on opposite sides of the fence for 90 minutes.

Mr Blair declined to be drawn on the prospects of going head to head with Mr Ahern for the job of European Union Commission President.

"No, I don't think I'll get into that one except to say that there is absolutely no job that this man could not do well," he said.