Congressman Patrick Kennedy, son of US Senator Ted Kennedy, has described as "opportunis tic, destructive and shocking" suggestions by Mr Raymond Seitz that Mrs Jean Kennedy Smith was an IRA apologist.
Speaking in Kinsale, Co Cork, yesterday Mr Kennedy said his aunt would be marked by history as one of the singular US ambassadors to Ireland. Her role in persuading President Clinton to visit here would be equally well received by the historians.
He was shocked and amazed that Mr Seitz, the US ambassador to London between 1991 and 1994, should have chosen this time to publish his memoirs, Over Here. The Sunday Telegraph began serialising the book at the weekend.
The publication of the extract, he added, had come at an important time in the peace process, but it was aimed at getting the maximum attention for his book.
"Unfortunately, this is a particularly bad time to be exciting fears and misunderstanding, and for someone whose main mission and training was to work towards a resolution of the Northern Ireland difficulties, his decision was outrageous and was a destructive one as far as the peace process is concerned.
"I am shocked that someone with his background in the American Foreign Service did not understand that there is a greater mission - and that is to be a representative for peace and reconciliation. He, more than anyone, should have understood this," Mr Kennedy said.
Mrs Kennedy Smith had in the past and was still espousing official US foreign policy. Because of her, President Clinton had brought more influence to bear than any other US president on steps towards a resolution of the Northern Ireland conflict.
Mr Kennedy said he was a member of the US National Security Council, which took a broader view of all issues. Mr Seitz, on the other hand, had taken a parochial and narrow-minded one.
Asked about the role played by Mrs Kennedy Smith in securing a visa to allow Sinn Fein president Mr Gerry Adams to travel to the US, he said she was a pragmatist and had recognised there could never be reconciliation unless all parties to the conflict were talking together.
Mr Kennedy said that the media had played up the fact that two of his fellow congressmen had published a joint statement opposing the latest document from the British and Irish governments on the grounds that it favoured the unionist stance.
There was great interest in the US in the events taking shape in Northern Ireland but there were disparate views. The common thread, however, was that everyone wanted peace to take hold.
"I believe that this is the time in history for this to happen in Northern Ireland.
"Like my father, I am not going to make any comment that might disrupt the peace process because right now, the smallest innuendo and nuance could cause things to come apart. Tensions are running very high and it is important for politicians to choose their words carefully," he said.