Ulster Unionist leader David Trimble is facing party hardliners who are urging a new deadline for Sinn Fein's exclusion from government.

Party MPs Jeffrey Donaldson and David Burnside want 1 July set as the date for the republican party's ejection from the executive.

Mr Donaldson said he believed the deadline was reasonable.

A key meeting takes place at the Ulster Unionist's east Belfast headquarters on Saturday.

David Burnside wants Sinn Fein excluded

The deadline call 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.

Mr Trimble said it was "no surprise", while Mr Donaldson said Sinn Fein was not fit to serve in the Northern Ireland Executive.

Mr Burnside, the South Antrim MP, said he wanted his party executive to back the 1 July deadline.

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.

We are not turning against Trimble, we are turning against the process

Fred Rodgers Ulster Unionist

"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.

The British and Irish Governments have now agreed to hold crisis talks over the peace process.

However, as they arrived, some executive members said they were unimpressed by the announcement of crisis talks.

Former Belfast City councillor Fred Rodgers, who has supported Mr Trimble in the past, said he believed a change in leadership was inevitable.

"If we do nothing and create another fudge and go into this election with Trimble as leader we are finished," he said.

"We are not turning against Trimble, we are turning against the process."

Assembly member Danny Kennedy confidence had to be restored in the political process.

"Clearly the government or the prime minister are either unwilling or incapable of doing something, I suspect unwilling," he said.

"We as a party must make a determined effort to see that appropriate sanctions are brought against the republican movement."

'Public domain'

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.

Nigel Dodds: Time to exclude Sinn Fein

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.

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.