The IRA has disposed of the largest consignment of its weapons so far, the head of the international decommissioning body, General John de Chastelain, has said.
The retired Canadian general confirmed a third act of decommissioning had taken place after briefing the British and Irish Prime Ministers, Tony Blair and Bertie Ahern, at Hillsborough Castle on Tuesday.
He said the quantity of arms put beyond use was "considerably larger" than that which had been previously decommissioned by the republican movement.
The news follows an IRA statement and the announcement of fresh assembly elections by Downing Street.
0710 BST: Downing Street announces 26 November election date
1030: Sinn Fein's Gerry Adams urges total support for political process
1215: IRA says there will be further act of decommissioning
1415: IRA says further act of decommissioning took place under agreed scheme
1600: Arms chief says a third act of decommissioning has been witnessed
Statements from Prime Ministers Blair and Ahern, Ulster Unionist leader David Trimble
"The commission has witnessed a third event in which IRA weapons are put beyond use in accordance with the government scheme and regulations," said General de Chastelain.
"The arms comprise light, medium and heavy ordinance and associated munitions.
"They include automatic weapons, ammunition, explosives and explosive material.
"The quantity of weapons involved was larger than the quantity put beyond use in the previous event.
"I do want to make the point - and that is why we have indicated this time - that the amount of arms put beyond use was larger - I would say considerably larger - than the previous event."
Andrew Sens, General de Chastelain's colleague on the commission, said: "The material put beyond use this morning could have caused death or destruction on a huge scale had it been put to use."
But the general also added the IRA had again exercised its option to restrict what detail he could reveal about the decommissioning act.
Earlier, Downing Street confirmed a 26 November poll date and the IRA issued a first statement saying it was committed to resolving the weapons' issue.
Northern Ireland's devolved administration was suspended a year ago amid allegations of IRA intelligence-gathering in the Stormont government.
In a second statement on Tuesday, the IRA leadership confirmed that more weapons had been decommissioned.
A spokesman said this had happened under the scheme agreed between the IRA and General de Chastelain.
It is understood there are plans for further meetings between the IRA and the arms body.
Ahead of the IRA statement, Sinn Fein President Gerry Adams urged total support for the political process.
In some of the strongest words the Sinn Fein president has used in support of the peace process, he said Sinn Fein was "opposed to the use or threat of force for any political purpose".
Mr Adams said: "Sinn Fein wants to see the guns taken out of Irish society."
Speaking to Sinn Fein election candidates, Mr Adams appealed to armed groups not on ceasefire, and particularly dissident republican groups opposed to the peace process.
"I appeal to them to join with the rest of us, republican and unionist, nationalist and loyalist in taking a leap forward together and collectively building a new future based on justice and peace."
He said unionists and republicans were working together to try to bring about a "full and final closure of the conflict".
Earlier on Tuesday, Tony Blair's official spokesman said it could be "the most significant day since the Good Friday Agreement".
He said what made it different was that the progress had been made between the parties themselves rather than the government driving the process forward with Mr Blair as "an interlocuter".
The announcement of an election date came after weeks of top-level negotiations between Sinn Fein and the Ulster Unionists, as well as the British and Irish Governments.
Assembly elections were postponed in May over what the government called a lack of clarity about the IRA's future intentions.
The British and Irish Prime Ministers, Tony Blair and Bertie Ahern, have arrived in Northern Ireland to give their approval to the deal.
Ulster Unionist leader David Trimble is expected to provide his initial response, probably confirming that he intends to bring any deal to his party's ruling council.
Reacting to the news of an election date, Michael McGimpsey of the UUP said within hours, unionists may know what republican intentions are about the future of the IRA.
SDLP leader Mark Durkan said a more inclusive approach should have been adopted.
The Democratic Unionist Party reacted with scepticism to Tuesday's
The party's deputy leader Peter Robinson said there was nothing new from Sinn
Fein or the IRA.
Gerry Adams had offered only "spin and hype", he said.
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