The Ulster Unionist Party must set a deadline for the exclusion of Sinn Fein from government, hardline South Antrim MP David Burnside has said.

The comments followed a security assessment that senior IRA leaders were aware that members of the organisation were using Colombia as a testing ground for new weapons.

Ulster Unionist leader David Trimble said it was "no surprise", while party colleague Jeffrey Donaldson said Sinn Fein was not fit to serve in the Northern Ireland Executive.

David Burnside wants Sinn Fein excluded

Mr Burnside said he wanted his party executive, which meets on Saturday, to set a 1 July deadline for a withdrawal from the executive if action is not taken against Sinn Fein.

Earlier on Friday, Mr Trimble called on UK Prime Minister Tony Blair to take action to prevent a "catastrophic loss of confidence" in the peace process.

"He has got to create confidence in the community in Northern Ireland that the law will be observed and will be enforced, and when republicans are found to be behaving in a way that is contrary to their undertakings, that he will act.

"There is no doubt that there are people in the republican movement who have been guilty of breaches of the ceasefire," said Mr Trimble.

Democratic Unionist Party MP Nigel Dodds said the British Government now had no choice but to take action against Sinn Fein.

"What more evidence is needed for the secretary of state and the pro-Agreement parties, particularly David Trimble, to act.

"It is no good turning a blind eye to these matters. They should join us in seeking to put Sinn Fein/IRA out of government," he said.

However, Sinn Fein's Gerry Kelly said they were "unfounded allegations".

SDLP chairman Alex Attwood said the reports should be treated with caution given that "these are unnamed security sources that may be putting into the public domain these allegations for uncertain reasons".

IRA leaders have denied authorising any action in the south American country, but unionist politicians say the latest security assessment points to a clear breach of the IRA's ceasefire.

The allegations over Colombia, and a security breach at Belfast's police headquarters linked to the republican group, have raised questions about the IRA's backing for the fragile Northern Ireland political process.

Michael McGimpsey: Allegations demand answers

On Thursday, the IRA repeated its denial that the leadership had sent anyone to Colombia to train or to engage in military co-operation with any group.

A spokesman said the group firmly rejected "unsubstantiated allegations" about IRA activity in Colombia which he said had come from "unnamed securocrats who had continually sought to undermine the peace process".

Rockets

But a security assessment given to the BBC suggests the IRA had been using Colombia as a training ground for its "engineering department" - to develop new types of weaponry, including rockets.

The assessment also deals with the issue of who in the IRA gave clearance for its south American involvement.

It says the IRA activities in Colombia were "definitely sanctioned at army council level" by the organisation's chief of staff Thomas 'Slab' Murphy and by Brian Keenan, who represents the group in talks with the international decommissioning body.

Security sources say he and a west Belfast republican, once labelled "Britain's most wanted woman", Evelyn Glenholmes, developed the link between the IRA and the left-wing Colombian guerrilla organisation FARC.

Meanwhile, the trial of the three Irishmen held in Colombia has been delayed.

The authorities have said they cannot guarantee their safety in court.

The rebel group FARC have threatened prosecutors and other public officials in the province where the trial had been due to take place in July.