David Trimble has rejected IRA accusations that unionists and the security services are trying to create a crisis in the peace process.

A meeting on Thursday between Trimble and the prime minister came ahead of a key gathering of the Ulster Unionist Party's ruling council on September 21, where there will be renewed questioning over whether to remain in the power-sharing executive with Sinn Fein amid doubts over the integrity of the IRA ceasefire.

In a bid to bring hard-line unionists on side, the government is expected to reveal next week that it will appoint an independent monitor of the paramilitary ceasefires.

Speaking after the meeting, Trimble said "We need more progress on independent monitoring of the ceasefire".

He indicated that the government appeared to accept in principle that there should be an independent auditor to restore confidence in the process.

With allegations of IRA involvement with Colombian terrorists, Belfast rioting and the Castlereagh security base break-in, hard line unionists have been pressing for the expulsion of Sinn Fein from the Ulster executive.

But in an interview with the republican An Phoblacht newspaper, a senior IRA source blamed unionists and parts of British military intelligence for trying to create a crisis in the peace process.

The IRA also rejected one idea being considered by the government, for an independent auditor to be appointed to rule on whether terror groups breach their ceasefires.

The spokesman said the proposal would only "serve the interests of those opposed to change".

And Sinn Fein chairman Mitchel McLaughlin, who has received death threats from loyalist paramilitaries, told the BBC that the appointment of an auditor would distract from the real issue of putting the work of the devolved assembly centre-stage.

"Does anyone think that an auditor is going to make my existence any safer?" he asked.

The nationalist SDLP, however, said the idea was "worth exploring".

And Trimble, the Ulster Unionist Party leader, said the IRA statement "marks a new and worrying phase in republican thinking".

"Anyone, unionist or nationalist, reading the full text of the interview could not be other than taken aback at the disingenuousness and maliciousness of the IRA spokesman. It comes as no surprise that the IRA accepts no responsibility for any of the problems in the political process.

"Their professed saintliness cuts no ice in any quarter. What is worrying is that the IRA seems to have reached a new level of unreality in its thinking and pronouncements," said Trimble.

He added that it was the IRA's failure to keep its own promises that had caused difficulties for the peace process.

The continuing pressure on the peace process, centred on unionist unease at the continuing activities of republican terror groups, has already prompted one concession from the government.

After meeting with Northern Ireland's police chief, Hugh Orde, on Wednesday, the prime minister backed the temporary retention of Northern Ireland's full-time police reserve.

But UUP assembly member Fred Cobain said the government must go further.

"The prime minister's reassurances that the Chief Constable will have the resources required to do his job are not enough in themselves," he said.

"Some time ago the government committed itself to tackling issues such as retaining the full-time reserve, providing additional money for training and a new police college.

"It is time for Mr Blair to honour these commitments," said Cobain.

The search for compromise was expected to continue when US president George Bush's special adviser on Northern Ireland, Ambassador Richard Haass, arrived in Ulster on Thursday.

He was expected to meet with senior party figures from both sides of the divide.