The Northern Ireland First Minister, Mr David Trimble, told the House of Commons that the Ulster Unionist Party could not continue in an administration with parties that were not committed to the Belfast Agreement.
Speaking after Mr Peter Mandelson's statement, he asked the Northern Secretary to confirm that unless there was "clear, significant and verifiable" decommissioning by the IRA, he would suspend the institutions set up under the agreement.
Without addressing the question, Mr Mandelson urged Mr Trimble not to take "precipitate action" in the coming days and allow events to unfold.
Asking the British government to proceed with caution, the Deputy First Minister, Mr Seamus Mallon, told Mr Mandelson that suspension of the Executive and the Assembly at this time and in the present circumstances would cause "serious and lasting damage" to the institutions of government in Northern Ireland.
The Shadow Northern Ireland Secretary, Mr Andrew Mackay, told MPs it was a "very sad day for the people of Northern Ireland" and they had been badly let down by the failure of the paramilitaries to decommission. He said many people would regret the suspension of the Assembly and the Executive, but it must be borne in mind that it was not of Mr Trimble's or Mr Mallon's doing. The Labour MP, Mr Tony Benn, urged Mr Mandelson "not to go back to the old direct rule" and raised the question of implementing a form of direct rule by London and Dublin. The DUP leader, the Rev Ian Paisley, urged Mr Mandelson to clarify the government's position that there would be no joint rule in Northern Ireland. He also insisted that if there was to be a "pause" in government, there should also be a pause in the release of paramilitary prisoners and the implementation of the Patten report.
Mr Mandelson said the British government did not support joint rule, however helpful it was to have the support of Dublin. He added: "If there is no decommissioning there will be no full implementation of the Good Friday agreement, there will be no devolution in Northern Ireland. It is a matter of colossal regret, but it is a fact."
In Belfast, political parties continue to pressurise the republican movement to make an eleventh-hour gesture on arms to prevent the suspension of the agreement's institutions.
Mr Mandelson's statement in the Commons was broadly welcomed by a senior Ulster Unionist Party figure, Mr Michael McGimpsey. While it was understood that the UUP leader's postdated resignation letter was dated for today, Mr McGimpsey, the North's Minister of Culture, Arts and Leisure, indicated last night he did not expect Mr Trimble to go ahead with his resignation today.
He appeared satisfied that the pledge to suspend the institutions next week in the absence by that stage of some IRA movement on arms would be sufficient to safeguard Mr Trimble's leadership.
Sinn Fein MLA and former IRA prisoner Mr Gerry Kelly expressed deep concern at Mr Mandelson's statement about introducing legislation to suspend the institutions. "What he is saying is he is going to put it into suspension, and I don't know how we are going to get out of suspension." Mr Kelly said it would be an "absolute disaster" to suspend the institutions, and he attempted to lay the blame for the current crisis on the UUP. "The threat to the peace process at this point in time is a political party [the UUP] refusing to work the institutions," he said.
Earlier, speaking before Mr Mandelson's statement, the Sinn Fein president, Mr Gerry Adams, said any suspension of the institutions would be contrary to the Belfast Agreement. Mr Adams and Mr Kelly said that throughout yesterday they engaged in intensive discussions to try to find a way out of the impasse.
Mr Sean Farren, the SDLP Minister of Higher and Further Education, said before Mr Mandelson's statement that now was the time for the paramilitaries, including the IRA, to move on weapons. "Will they cross the threshold into democracy and leave their weapons behind them, so that the rest of us can get on with living normal lives free from terror and fear, or will they hang on to them and condemn us to more uncertainty, more worry, more fear? Their day has come. It's up to them." The Ulster Unionist Party MLA, Dr Esmond Birnie, dismissed what he called the fallacious arguments from republicans justifying non-decommissioning. Dr Birnie said IRA guns had not "been silent" and some also were passed on to republican dissidents.
Alliance indicated that the party would oppose Sinn Fein taking the lord mayoralty of Belfast City Council in June if there were no decommissioning by May 22nd, the suggested date for disarmament in the agreement.