Story Highlights• NEW Six and eight devices defused at Northern Ireland's parliament
• Pro-British convicted killer Michael Stone arrested after breaching security
• Protest takes place as talks held on restoring power-sharing government
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BELFAST, Northern Ireland (CNN) -- Six and eight devices have been discovered and defused at Northern Ireland's parliament, police said on Friday, hours after a militant breached security at the building.
Northern Ireland's Chief Constable Hugh Orde said the explosives were found in a bag that convicted killer Michael Stone threw into the lobby of Stormont Parliamentary Building.
Orde told a news conferences they were "viable" devices and that their potential for causing damage, death and injury was being assessed. (Watch as man breaches security at Stormont -- 2:08)
"They are fairly amateurish in design, that does not make them any less dangerous," he added.
Orde said a gun and a knife was also found. Stone was arrested and was being questioned by police on Friday night about what the chief constable branded "a sad publicity act by a very sad individual."
The incident took place as talks were being held on renewing the currently suspended self-rule government for Northern Ireland in which pro-British and pro-Irish opponents would share power.
"A man pushed his way through the revolving doors. He had a bag with him. He threw the bag into the security search pointed and shouted it was a bomb," said Stephen Hird, a photographer for the Reuters news service.
In the video shot by Hird, Stone was wrestled to the floor by security officers, who said they were treating his bag as a "live device."
In the past, Stone has served a prison term for opening fire on mourners at an IRA funeral in 1988, killing three people. (Profile)
Stone is staunchly opposed to such a power-sharing government and supports British rule in Northern Ireland.
Friday was a deadline imposed by London for hard-line Protestant leader Ian Paisley and Martin McGuinness, deputy leader of Sinn Fein, the largest Catholic party, to be nominated to serve in the top two power-sharing posts.
The event would have been purely symbolic, because the full administration would not be given powers until March.
Journalist Peter Taggart contribubed to this report.