Updated

Northern Ireland's Sinn Fein party urged the Irish Republican Army to begin disarming Monday in an effort to save the peace process.

Leaders of the main Protestant party, the Ulster Unionists, have resigned from Northern Ireland's government to protest the IRA's failure to keep its promises to put its weapons "beyond use."

The Belfast government, an experiment in Catholic-Protestant power-sharing, could collapse within days.

If the IRA did begin to disarm, Ulster Unionist leader David Trimble said he and his party's three other Cabinet ministers would resume their posts.

The Ulster Unionists have twice agreed to join administrations including the militant Roman Catholics of Sinn Fein, on condition that IRA disarmament followed. The IRA has yet to fulfill a May 2000 pledge to disarm.

Sinn Fein President Gerry Adams said he and his deputy, Martin McGuinness, both urged the step.

"Martin McGuinness and I have also held discussions with the IRA and we have put to the IRA leadership the view that if it could make a groundbreaking move on the arms issue that this could save the peace process from collapse and transform the situation," Adams said.

Adams said Monday that he did not underestimate the difficulty of the issue for republicans, as IRA supporters are known.

"The IRA is not an organization that bows to pressure or which moves on British or unionist terms," he said.

"IRA volunteers have a view of themselves and a vision of the Ireland they want to be a part of. This is what will shape their attitude to this issue. Republicans in Ireland and elsewhere will have to strategically think this issue through."

He appealed to IRA supporters to stick together.

"It is a time for clear heads and brave hearts. The IRA must stand out as an example of a people's army, in touch with the people, responsive to their needs and enjoying their genuine allegiance and support."

Earlier, Britain's Northern Ireland Secretary, John Reid, said a republican move on disarmament would not receive a "grudging or ungenerous response" from the government.

"I do not underestimate the difficulties for paramilitary groups in resolving the issue of arms," Reid said. "Nor do I underestimate the significance of the steps they have already taken. They are being asked to enter a new historical dynamic."

"So I want to say to the paramilitaries: If you are able to do what the people of Northern Ireland want so desperately — to put arms beyond use and to take politics on to a new plane — then I believe you will not find the response from this government, from the Irish government, the American administration and the whole international community to be grudging or ungenerous."

The Associated Press contributed to this report.