British army experts defused at least six explosive devices delivered by a Protestant extremist to the Northern Ireland Assembly, the province's police commander said Friday.

Chief Constable Hugh Orde said the explosives inside the bag, which convicted killer Michael Stone threw into the lobby of Stormont Parliamentary Building during a debate on power-sharing, were "fairly amateurish in design. That does not make them any less dangerous."

Police subdued Stone, who killed three people at an Irish Republican Army funeral in 1988, after he tossed a bag into the building and claimed it contained a bomb.

Politicians and journalists were ordered out of the building as the fire alarm sounded — and two security guards pinned Stone by both arms to the main doorway. He was later wrestled outside, into pouring rain and wind, as he shouted a favored Protestant militant slogan: "No surrender!"

British army experts examined the suspicious bag in the foyer of Stormont Parliamentary Building, but did not immediately confirm whether the bag contained explosives. Stone had tossed it at the building's security checkpoint staff, who operate metal detectors and search bags. He also appeared to have been spray-painting the entrance to Stormont with "Sinn Fein-IRA murderers" or "war criminals," but did not finish it.

Northern Ireland Secretary Peter Hain ordered an immediate investigation into what he called a "very serious breach of security."

Stone's demonstration came minutes after Protestant leader Ian Paisley refused to accept a nomination as the future leader of Northern Ireland's power-sharing administration.

Paisley, whose Democratic Unionist Party is the largest in Northern Ireland, said he would work with Sinn Fein, the IRA-linked party that represents most Catholics, only when it begins to support the police force. If that happened, Paisley said, he would accept the post.

"When Sinn Fein has fulfilled its obligations with regard to the police, the courts and the rule of law, then and only then can progress be made. There can and will be no movement until they face and sign up to their obligations," Paisley told the assembly.

The prime ministers of Britain and Ireland, Tony Blair and Bertie Ahern, said Stone's threat illustrated why rival British Protestant and Irish Catholic politicians should compromise and form a stable coalition as the Good Friday peace accord intended.

More than seven months ago, Blair and Ahern announced that Nov. 24 would be their final deadline for a power-sharing deal — but both on Friday shrugged off this commitment and insisted that Paisley's statement contained the hope of future progress.

Both premiers said they expected Sinn Fein to clear the way for Paisley by accepting the authority of the Police Service of Northern Ireland. Sinn Fein insists it will not take this step first, if at all.

"It seems that Michael Stone has gone on the rampage again, in a very dangerous way. But he was stopped," Ahern said in Dublin. "It just shows you exactly what we are trying to get away from in Northern Ireland."

Blair, who has closely cooperated with Ahern in brokering compromise in Northern Ireland since both premiers rose to power in 1997, said progress in Northern Ireland was difficult "because each step towards a different and better future is taken alongside the memory of a wretched and divisive past."

Stone is the living embodiment of one of Northern Ireland's most dramatic days — March 16, 1988, when he launched a solo gun-and-grenade strike on an IRA funeral. He killed three mourners, among them an IRA man, and wounded about 60 other people before a pursuing Catholic mob surrounded and badly beat him.

Stone was paroled from prison in 2000 under terms of the Good Friday pact, which permitted early releases for more than 500 convicted members of the IRA and outlawed Protestant paramilitary groups. He launched a career as an artist and also took part in a televised discussion, moderated by South African Archbishop Desmond Tutu, with relatives of a Catholic man he had shot to death in a different attack.

Friday was supposed to be the deadline for Paisley and Sinn Fein deputy leader Martin McGuinness to be nominated to the top two power-sharing posts. The event would have been purely symbolic, because the administration is not scheduled to be formed and given powers until late March.

Despite Paisley's refusal, Hain said his words were sufficient to keep the assembly intact until the end of January, when Britain plans to dissolve it anyway.

An election to a new assembly is scheduled March 7. Britain expects the members to elect all 12 members of the administration, to be led by Paisley and McGuinness, on March 14. If this happened, Britain would transfer control of Northern Ireland's 13 government departments to the administration March 26.