The IRA's decision yesterday "represents a new day of liberation for all the people of Northern Ireland", Senator Ted Kennedy said, following a meeting on Capitol Hill with Sinn FΘin's Mr Martin McGuinness.
It was a day of hope that would be seen as enormously heartening in the US and all over the world, he said.
Leading Irish-American politicians joined with the Administration in paying tribute to what all agreed was a breakthrough, and called for a generous response by other parties to the peace process.
A spokesman for the State Department, Mr Richard Boucher, described the decision as historic, and said they would await verification from the Independent International Commission on Decommissioning.
Asked if the announcement meant Sinn FΘin was "off the hook" for its involvement in Colombia, Mr Boucher said the US still required organisations to end their involvement with terrorism around the world.
Congressional sources suggest that the IRA decision will lead to an easing of pressure for a public inquiry on the issue.
Senator Chris Dodd, who met Mr McGuinness with Mr Kennedy, said that "in otherwise dark days here at home, I believe there is a possibility we can have some permanent progress in Northern Ireland".
Asked if he had received any assurances from Sinn FΘin that another escapade in Colombia would not happen again, Mr Dodd replied: "Yes."
He said Mr McGuinness expressed deep anger at the presence of the three men in Colombia and at the fact that he had not been made aware at the time they were going.
The chairman of the Friends of Ireland group, Mr Jim Walsh, a member of the House from New York, said that he appreciated that the republican movement was taking big risks.
But they had put their faith in democracy and now needed the rest of Northern Ireland to respond generously.
Mr Richie Neal, a member of the House from Massachusetts, described the announcement as "most extraordinary" and hoped that "this act of goodwill will be met with more goodwill".
Mr McGuinness, speaking outside Congress just after the IRA's announcement, paid tribute to what he called a "courageous", "unprecedented", and "truly historic" decision by the IRA that "could bring a turning point in the troubled history of Northern Ireland".
"This is a great day for Ireland," he said.
He said the act of good faith by the IRA should now allow the decommissioning body to carry out its remit and allow the institutions to get on with their job.
"Arms were used [by Unionists] as an excuse," he said, to hold up progress.
All he wanted to do was get back to his own job as Minister for Education.
Mr McGuinness called on the British government to respond by reducing the level of their military presence and, among other measures, remove the observation towers "to let the people of South Armagh have their countryside back".
