Sinn Fein says a legal challenge is possible over government moves to suspend the Northern Ireland Assembly and power-sharing executive.

The Northern Ireland Secretary Peter Mandelson has said direct rule from London will be resumed late next week, unless there is a significant move towards IRA disarmament.

Sinn Fein assembly member Alex Maskie said a legal challenge was being considered by the party.

"We believe these decisions by the British government are very dubious and suspect in terms of the law and the [Irish] constitution."

The IRA is under enormous pressure to begin the process of decommissioning, but says it will not do so on either British or unionist terms.

In a speech on Sunday the Prime Minister Tony Blair said the issue of weapons would not disappear, and had to be confronted.

"I'm not standing here as the British prime minister making demands. I can't make anybody do this. We just need to know whether it is going to happen or not."

He said: "If we let this chance for peace go, if we let fall from our fingers the very thing we had grasped so firmly - the hope and chance of a peaceful future for the children of Northern Ireland - then we will have failed the people we serve and that would be the biggest betrayal of all."

Republicans have taken soundings which, they say, suggest Mr Mandelson would act in breach of the Good Friday Agreement, if he suspends the devolved government.

The latest threat to bring the ongoing dispute over the arms issue to court was also hinted at by Sinn Fein chairman Mitchel McLaughlin, during an interview on BBC 1's On The Record programme.

He insisted the current crisis was not about the arms issue.

"It's about the fact that there's a unilateral threat to walk away from the political process and, in response, the British Government, it appears, is prepared to enter into default of the Good Friday Agreement to give cover to David Trimble."

He said the British Government threat to re-impose direct rule by the end of this week in the absence of IRA decommissioning would be "counter-productive".

Mr McLaughlin said his party was committed to achieving the goal of decommissioning.

"My party will work strenuously to meet that deadline - we have to try and do in five months what we originally gave ourselves 24 months to achieve," he said.

When asked if the party wanted more time to convince the IRA to disarm by May, he said: "I believe we can meet the deadline."

Meanwhile, a senior Ulster Unionist has indicated a possible shift in the party's position on decommissioning.

Speaking on BBC Radio Ulster's Seven Days programme, Dermot Nesbitt said the party wanted a successful outcome to the process.

"Decommissioning can take place by the IRA self-destroying and verified by General de Chastelain.

"We are not hung up on how they are destroyed," he said.

Mr Nesbitt's comments came in the middle of a day of intense media interviews and articles involving the main participants.

'Moral obligation'

Writing in the Belfast-based newspaper, the Sunday Life, the Ulster Unionist leader David Trimble said he wants republicans in the process, but not at any price.

The First Minister challenged the republican movement to choose between politics or paramilitarism. "Is it to be the party or the army, they cannot have both in a democracy?" he asked.

Mr Trimble's article follows an IRA statement on Saturday over the deadlock in weapons decommissioning, which met with a lukewarm response from both the Irish and British Governments.

Sinn Fein president Gerry Adams, writing in the same newspaper, said he was now in the difficult position of shuttling between the IRA and others in an effort to avert current impasse. He said he believed there was a moral obligation to avert the current crisis.

"One thing is certain, the process does not have to collapse," he said. "It can be saved if the political will exists."

The arms issue is threatening to bring down Northern Ireland's fledgling power-sharing government, unless there is movement by Friday of next week.

The IRA issued a statement on Saturday saying the arms issue "will not be advanced by British legislative threats".