Richard Haas: 'Extraordinarily pleased for the people of Northern Ireland'
Richard Haas told BBC Two's Newsnight programme that the White House congratulated the IRA for its "historic" decision and thanked the head of international body charged with dealing with paramilitary weapons, Gen John de Chastelain.
"This opens up tremendous possibilities for peace in Northern Ireland," Mr Haas said.
"We hope it is responded to in a very positive and generous way and people take advantage of the opportunity that this has brought about," he added.
Speaking from Washington, Mr Haas continued: "This is something that Republicans and Democrats have worked for in this country for years, and we are extraordinarily pleased for the people of Northern Ireland.
"Our hats also go off to the British and Irish Governments for playing such a useful role behind the scenes in helping to bring this about," he added.
This is the first time that an Irish republican group which has violently resisted the British presence in Ireland has ever disposed of weaponry in this way.
Mr Haas told the programme that the 11 September suicide hijack attacks on the US had "underscored the necessity of change".
"What we have heard since 11 September in this country is a growing number of statements by prominent Irish-Americans - long-term supporters of Sinn Fein - saying that whatever good or bad may have come from guns in the past, the time has come to put arms verifiably beyond use," he said.
"The IRA had begun to go down the path of transforming itself from a paramilitary organisation into something else, and 11 September helped crystallise the necessity of continuing to go down that path," Mr Haas continued.
"The situation in Northern Ireland today is much better than it was several years ago, and this will make it much better yet several years from now," he predicted.
Long-awaited move
The IRA move - long demanded by unionists - seems certain to breathe new life into the troubled peace process which had reached a crisis-point over decommissioning.
Mr Haas said: "This step was necessary to save the devolved political institutions so that the people of Northern Ireland can increasingly govern their own lives.
"People see the good things that have come from the Good Friday Agreement and simply calculated that this was the natural next step to take," he added.
Mr Haas described the Agreement as "a comprehensive well-designed package in which everybody gives and everybody gets".