BELFAST, Northern Ireland -- Capping a three-month mission to save Northern Ireland's peace accord, American diplomat George Mitchell said Thursday the IRA must start disarmament talks the same day a Protestant-Catholic administration is established.

"Neither side will get what it wanted and both will endure severe political pain. But there is no other way forward," he said.The former U.S. Senate majority leader, who helped achieve the 1998 Good Friday accord and returned to resolve an impasse over Irish Republican Army weapons, presented his conclusions to seven pro-agreement parties at the Belfast negotiating venue.

In a crucial development Wednesday, the IRA promised to send a negotiator to a disarmament commission if the British-ruled province's major Protestant party, the Ulster Unionists, first formed the joint administration envisaged in last year's accord.

The policy turnaround came after Ulster Unionist leader David Trimble dropped his insistence that the IRA start handing over weapons first. Trimble said the IRA statement would be sufficient for him to accept the IRA-linked Sinn Fein party within a new Cabinet, long the stumbling block to peace progress.

Mitchell said all now appeared in order to implement the Good Friday accord.

"Devolution should take effect, then the executive should meet and then the paramilitary groups should appoint their authorized representatives, all on the same day, in that order," he said.

The IRA statement offered no explicit guarantee that gradual disarmament will follow. But until now the outlawed movement had rejected any direct contact with the disarmament commission, formed in 1997 during peace negotiations.

"There has been a lot of talk about guarantees," said Mitchell. "Well, there is one guarantee: It is if this process fails, there will be no chance whatsoever for any decommissioning."

John de Chastelain, the Canadian general who leads the disarmament commission, is expected to confirm whether or not the IRA had begun identifying the whereabouts of its many weapons dumps.

Gerry Adams, leader of the IRA-allied Sinn Fein party, described Mitchell's statement as promising, but said testing times remain ahead.

"It is also very much about proving ... that politics works and politics can bring about change. And that will be the big test," Adams said.

In the past IRA commanders had argued that to hand over even a single bullet would symbolize surrender, and humiliate and split their ranks. After the most recent round of negotiations, Sinn Fein and the IRA appear at their most likely ever to actually deliver disarmament.

IRA splinter groups still scheming to unravel the IRA's 1997 truce, remain marginalized because of their car-bomb attack on the town of Omagh last year that killed 29 people -- the deadliest terrorist strike in the past three decades of bloodshed.

Trimble, the Nobel Peace Prize laureate elected to lead the Cabinet, faces a far more serious challenge in the immediate future. His decision to soften his "no IRA guns, no government" policy needs approval by a majority of the Ulster Unionists' 800-strong ruling council. The vote is expected Nov. 27.