Mr Gerry Adams has said he understands why unionists are demanding decommissioning now, but they must be patient because the Provisional IRA cannot be forced to act quickly.
The Sinn Fein president appeared to rule out any chance of an arms handover before the chairman of the international decommissioning body, Gen John de Chastelain, issues his report on Monday.
In a speech last night Mr Adams said it would be a mistake if the Executive collapsed and the First Minister and the other UUP members resigned over the decommissioning issue.
He was speaking as he opened new party offices in Newry, Co Down.
"I understand why unionists and others want decommissioning now. I can see it from the unionist point of view.
"But non-republicans need to see this issue from the IRA's point of view. It is not easy to get the IRA, or indeed any of the armed groups, to do this speedily. This is the reality . . . So there is a need for unionism to be patient and for people to have faith."
Mr Adams said he was committed to disarmament and believed decommissioning was achievable, but only as a voluntary process.
He insisted he had never misled anyone into thinking Sinn Fein could deliver on decommissioning.
All the party could do was use its influence, he added. There had been no secret deals.
The Ulster Unionist Party's decision to set a deadline of February for the start of decommissioning had made progress on the matter even more difficult.
"There should be no doubt of how badly the February deadline damaged our efforts. It is a fundamental mistake in strategy to try and force decommissioning by seeking to marginalise a political party and its electorate.
"I remain committed to decommissioning as an essential part of the peace process and I will continue to work to try and bring this about.
"But I have to say that the achievement of this objective has been set back by the way it is being used as a political football by unionists at this time."
There has been speculation the British government could suspend the North's new Executive and reintroduce direct rule from Westminster next week.
Mr Adams said this would only create a dangerous political vacuum, encouraging anti-agreement unionists and placing the entire peace process in jeopardy and making decommissioning even more difficult than it had been so far.
Responding to speculation that the British government was considering another review of the implementation of the Belfast Agreement, Mr Adams said the only basis for this would be if there had been a default on decommissioning, which there had not been.
The Belfast nationalist newspaper, the Irish News, has said it is time the Provisional IRA moved on decommissioning. The newspaper said nationalists would be "appalled" if a failure to decommission led to the collapse of the new Executive.
In a rare front-page editorial, the paper said there could be no doubt about the mood within nationalism and that the retention of a full arsenal could not be justified.
"The vast majority of nationalists want to see the decommissioning issue resolved immediately and the Executive not only preserved but strengthened," it said.