"The leadership has formally ordered an end to the armed campaign," the IRA said in a statement released in Belfast. "All Volunteers (the IRA's name for its soldiers) have been instructed to assist the development of purely political and democratic programs through exclusively peaceful means."

The IRA gave no reason for the timing of its announcement. The underground army and its allies in Sinn Fein, the group's political wing, have been on the defensive since December, when police accused its members of carrying out a $50 million robbery of a downtown Belfast bank.

In January, the IRA drew international criticism after acknowledging that several of its members took part in the fatal stabbing of a Catholic construction worker outside a Belfast bar.

The IRA traces its roots to a Dublin rebellion against the British in 1916. In 1997, the IRA declared a cease-fire, which suspended nearly 30 years of fighting in Northern Ireland. About 3,600 people had been killed in that period.

Northern Ireland is a Protestant-majority segment of the United Kingdom formed after most of Ireland was given nominal independence in 1921.

In its statement, the IRA said it will continue to work for a united and independent Northern Ireland using non-violent methods.

The IRA's announcement was met with guarded praise from British, Irish and U.S. leaders. In a joint statement, Irish Prime Minister Bertie Ahern and British Prime Minister     Tony Blair said the IRA's words must be "borne out by actions" and must also include an end to "criminal activity."

White House spokesman Scott McClellan said the statement was "potentially historic." He called on international monitors to verify the IRA's "commitments" to disarm.

But the Rev. Ian Paisley, leader of the mostly Protestant Democratic Unionist Party, Northern Ireland's largest political group, noted that the IRA had made many so-called "historic" statements over the past decade. "These same statements were followed by the IRA reverting to type and carrying out more of its horrific murders and squalid criminality," he said.

In Washington, Martin McGuinness, chief negotiator of Sinn Fein, acknowledged that winning over Paisley and Northern Ireland's Protestants is key to the success of the IRA's peace strategy.

He called on Paisley to "accept our hand in friendship" and to help revive Northern Ireland's power sharing local government, which has been suspended since 2002 because of Protestant protests about crimes and other IRA activities.

Mitchell Reiss, U.S. special envoy to the Northern Ireland peace process, said that the IRA's decision appears to have been at least in part a response to the backlash from the murder outside the pub and the bank robbery.

The five sisters and fiancée of the victim, Robert McCartney, were welcomed by     President Bush at the White House on St. Patrick's Day. For the first time in a decade, Sinn Fein President Gerry Adams was not invited.

In Belfast, the battleground for much of the war, reaction was underwhelming. Unlike 1994, when the IRA declared a cease-fire, there were no spontaneous street parades led by drivers of the city's distinctive black taxi cabs.

"People sort of took it in stride," said Sammy Douglas, a community organizer in Protestant East Belfast with contacts in the Catholic neighborhoods. "We've sort of been here before, so people are waiting to see if the IRA are as good as their word.

"Beside, after 9/11 and the state of terrorism in the world and all, the feeling was: What else could they do?"