Negotiations among rival Northern Ireland parties ended Saturday with no agreement to revive a Catholic-Protestant administration, but British Prime Minister Tony Blair insisted that a deal might yet be achieved.

As tired delegations departed from Leeds Castle, the magnificent, moat-encircled venue for talks that began Thursday, most factions suggested that the outlawed Irish Republican Army now held the initiative.

A statement from the underground group, expected to detail its conditions for disarming and renouncing violence, may come within a week.

Without sufficiently clear-cut commitments, the Democratic Unionist Party insists it will never share power with Sinn Fein, the IRA-linked party that represents most of Northern Ireland's Irish Catholics.

"I am too old to be bluffed. We say, we will believe it when we see it. And we're going no farther than that," said the Rev. Ian Paisley, 78, whose Democratic Unionist Party represents most of the British province's Protestant majority.

Blair and Irish Prime Minister Bertie Ahern -- who oversaw Northern Ireland's Good Friday accord of 1998 and have spent two years trying to revive its central goal of power-sharing -- stood side by side inside the castle as the delegations filtered out separately. They looked fatigued but tried to sound optimistic.

Blair said negotiators had "not yet achieved a comprehensive agreement" but insisted that lower-level talks next week would continue. "There is huge potential in what has happened here," he said.

"We believe we can resolve issues to do with ending paramilitary activity and putting weapons beyond use," Blair said. "We believe what is now on offer is reasonable in substance and historic in its meaning."

Blair said Sinn Fein-IRA leaders "know exactly what is required if they want to move this process forward. We will have to wait to see what response we get."

The U.S. envoy for Northern Ireland, Mitchell Reiss of the State Department, said he was also optimistic that a deal could be worked out in coming weeks.

Irish Prime Minister Bertie Ahern, left, and Britain's Tony Blair at talks.