The Northern Secretary, Mr Mandelson yesterday called on Sinn Fein to return to the negotiating table. He said he was glad that the republican movement was concentrating on "electoral politics and not the use of guns", but all weapons had to be put beyond use.
"That is what we have to sort out one way or the other. I want Sinn Fein to come back to the table and start talking again with their partners in this process to see if we can find a way forward," Mr Mandelson said.
A UUP Assembly member, Mr Ken Maginnis, said the decommissioning issue was not a matter solely between his party and Sinn Fein. "Gerry Adams has said this is a defining moment. It is a defining moment but for constitutional Irish republicanism.
"The parties in the South and the SDLP have to decide whether they are going to side with Sinn Fein or take a principled stand on the decommissioning issue," he said.
Sinn Fein held low-key roadside pickets in Belfast and Derry at the weekend, demanding the reinstating of the Assembly and the Executive.
Its president, Mr Gerry Adams, warned there could be a lengthy political vacuum. "The republican well is dry," he said. "Even though I'm not prepared to go chasing my tail as we have for the past 18 months, at the same time we're totally wedded to this process.
"Peter Mandelson has said this suspension can be ended and the institutions can be reinstated as easily as they were suspended. If that is the case then let him do that."
Meanwhile, Republican Sinn Fein opened its first office in Belfast at the weekend. About 50 people attended. The Republican Sinn Fein president, Mr Ruairi O Bradaigh,
claimed his party could gain from the political stalemate. "There is a window of opportunity open to us at the present time. What we are seeing is a battle for the hearts and minds of the people," he said.
"Others may have been sucked into the British system but we have not turned our back on any principles. We do not take part in administering British rule. We resist it."
On Sinn Fein's call for demonstrations to reinstate the Assembly and the Executive, Mr O Bradaigh said true republicans would not be on the streets demanding a return to Stormont.
When asked to comment on recent Continuity IRA bomb attacks in the North, Mr O Bradaigh said his party refused to comment on specific incidents but upheld "the right of the Irish people to engage in controlled and disciplined force to resist English rule in Ireland".
The DUP deputy leader, Mr Peter Robinson, said the SDLP must choose whether it is a party of "democrats or Provo puppets". Speaking in Omagh, he said: "When May comes without decommissioning, the process lies in the hands of the SDLP. It is time for the SDLP to come out from behind the republican movement. It is time it stood up to Sinn Fein and the IRA."
He said: "It is time the SDLP showed some leadership to the nationalist community. If they fail they will be destroyed by military republicanism."