Ulster Unionist leader David Trimble's party has announced the date of the crucial meeting to review progress on IRA decommissioning which could decide if it remains in government.

The meeting of the Ulster Unionist Council will take place on 12 February.

If there has been no decommissioning by the IRA by that time, the Council could pull Northern Ireland First Minister David Trimble and his ministerial colleagues out of the recently formed power-sharing Assembly Executive.

If that decision was taken at the February meeting, it would effectively plunge Northern Ireland into another political vacuum.

The announcement was made by the party's president Josias Cunningham.

He said: "We are calling a meeting in the expectation of John de Chastelain producing a report by the end of January.

"He said that he would do so and I have every confidence that he will do so."

Soon after the announcement of the date for the UUC meeting, dissident Ulster Unionist MP William Thompson said rank and file party members would be demanding "actual disarmament" in return for the executive's survival.

"Let there be no doubt. The party expects decommissioning to have taken place if the executive is to continue.

"That means when General de Chastelain's commission reports back at the end of the month, decommissioning must have taken place.

"Otherwise, our ministers will be resigning from the executive."

Mr Thompson said he understood if the de Chastelain report indicated no IRA decommissioning had taken place, letters of resignation for David Trimble and the party's ministers in the executive would come into effect on the day of the council meeting.

On Thursday, Mr Trimble called on republican paramilitaries to begin decommissioning in the next few weeks.

He was speaking following a meeting at Downing Street with the Prime Minister, Tony Blair, to bring him up to date on the latest political developments in the province.

'Onus on paramilitaries'

He said the onus was now on paramilitary groups to take the peace process forward.

Power was devolved to the Northern Ireland Assembly last month after the Ulster Unionist Council backed the peace deal brokered by former US Senator George Mitchell.

It allowed the Ulster Unionist Party to enter into government with Sinn Fein before the handover of terrorist weapons but also set a deadline of February for Mr Trimble to decide whether there had been enough progress made in decommissioning to continue supporting devolution.

The latest report from the international body on decommissioning is due later this month and Mr Trimble said he would like to see progress by the paramilitaries before then.

But Sinn Fein President Gerry Adams warned that ultimatums will not work in relation to IRA disarmament.

Speaking after a 45-minute meeting in Washington with US President Bill Clinton on Wednesday, Mr Adams called on Mr Trimble to "be leaderly" in helping to move the peace process forward.