Trimble's resignation casts doubt on future of Good Friday peace accord.(Chicago Tribune)

LONDON_Northern Ireland braced for a summer of political turmoil Sunday after the resignation of the province's first minister, David Trimble, cast into doubt the future of the Good Friday peace accord.

The groundbreaking political assembly established by the 1998 accord, in which Northern Ireland's four rival political parties shared power in the British province for the first time, is effectively on hold pending negotiations on its uncertain future.

Speaking in Thiepval, France, Trimble said he would return to his post at the helm of the power sharing body only if the Irish Republican Army takes steps to dismantle its military arsenal. "I'm prepared to resume that office, but only if we get this issue settled, and if we see weapons being put permanently beyond use in accordance with the decommissioning legislation," Trimble said during ceremonies Sunday commemorating Northern Irish soldiers killed in the World War I Battle of the Somme.

Trimble, chief of the Ulster Unionist Party, said he did not want to jeopardize the peace process but rather to put pressure on the IRA to comply with the provisions of the accord. "I'm stepping down as first minister in order to ensure the agreement is fully implemented," he said.

Trimble, who shared the Nobel Peace Prize for his part in leading Protestant loyalists into the historic peace agreement with their Catholic neighbors, had vowed he would resign July 1 if the IRA failed to comply with a June deadline for disarmament, and he did so early Sunday morning.

But Trimble's gamble that his resignation will force the IRA's hand may backfire. Leaders of Sinn Fein, the IRA-linked political party, were defiant Sunday, with its chairman, Mitchel McLaughlin, insisting the group "will not respond to blackmail." He called on Ulster unionists to find a new leader as well as a new approach.

So far there is no sign that the IRA is prepared to give way, and the political vacuum created by his departure risks heightening sectarian tensions at a critical moment in the political calendar.