David Trimble has said he would consider resigning again as Northern Ireland's first minister to make progress with the Good Friday Agreement.

The Ulster Unionist Party leader said he would be happy to quit if it was necessary.

Some members of his party have been calling for a withdrawal from the power-sharing executive if the British Government fail to exclude Sinn Fein from the executive.

It followed revelations on Thursday that security sources believe the IRA had been testing new weapons in Colombia.

Blair and Ahern have called crisis talks

Three Irishmen are in custody in the South American country awaiting trial on charges of training left-wing FARC rebels.

Mr Trimble said the IRA was in breach of the Agreement following the allegations about Colombia and involvement in the recent violence in the Short Strand area of east Belfast.

"If I do it, it will be in order to make progress, to make further progress in order to ensure the agreement is fulfilled and fully implemented," he said.

'Constraints'

Speaking on the BBC's On The Record programme, the first minister also accused the government of putting "political constraints" on police over its handling of recent violence.

He said police had failed to return former republican prisoners, released under the terms of the Good Friday Agreement, back to jail for being involved in the violence in east Belfast.

But Northern Ireland Secretary John Reid denied any interference in how the police had done their job.

"There are no political constraints on the police doing their job. They have to pursue that job wherever it leads them."

Dr Reid admitted there was a problem with the peace process at the moment.

"That is that there is a lack of confidence, that the journey away from violence towards exclusively peaceful means is continuing and that is why we have taken urgent action."

UK Prime Minister Tony Blair and Irish counterpart Bertie Ahern have agreed to convene crisis talks of the pro-Agreement parties within the next few days.

It is understood talks will concentrate on trying to resolve the current difficulties in the process and questions raised about the ambiguities of the present paramilitary ceasefires.