The IRA announcement was hailed this evening by the White House as potentially historic.
White House spokesman Scott McClellan said that the statement "must now be followed by actions demonstrating the republican movement's unequivocal commitment to the rule of law and to the renunciation of all paramilitary and criminal activities."
Speaking in the Senate, Democratic Senator Edward Kennedy that he hoped the statement meant the long process was nearing an end to take "guns and criminality out of politics in Northern Ireland once and for all."
Mr Mitchell Reiss, US special envoy to Northern Ireland, called the IRA pledge "a good first step", apparently driven by a public backlash to the McCartney murder and the Northern Bank robbery last December.
"What we don't know is whether it's truly historic and we'll find that out in the next weeks and months as they translate words into deeds on the ground," he said.
President George W. Bush's special envoy on Northern Ireland, Mitchell Reiss, described the statement
Mr Reiss was briefed on developments in Washington this morning by Sinn Féin chief negotiator Mr Martin McGuinness and said he had been encouraged by what he was told.
Republican congressman Mr Peter King branded the breakthrough "a truly defining moment in Irish history".
He said it was the "most dramatic step forward in advancing the peace process". Mr King, a leading Sinn Féin supporter, said he had been told two large IRA arms caches would be destroyed later in the day, but he said he did not know where.
"I can understand the unionists having some scepticism, which is why I think it will take several months to go back into government, but there's no reason negotiations can't start immediately," he said.
Mr King said he believed pressure from the White House and members of Congress had given the IRA a needed push.
"I think they were going in this direction anyway, but the process had become stalemated," he added. "I think the pressure from the US actually helped Gerry Adams and Martin McGuinness convince elements in the IRA that this had to be done."