After an hour of talks at Stormont both sides emerged saying little progress had been made on resolving the impasse surrounding decommissioning.

But Sinn Fein chief negotiator Martin McGuinness said he did not view the meeting as a set back but he called on Prime Minister Tony Blair to "liberate" Mr Trimble from the position he had adopted on the disposal of terrorist arms.

He said: "Our position is that we don't accept the position adopted by the Ulster Unionist Party.

"We can understand the context in which it evolved but we regard it as a serious mistake."

David Trimble: Demanding movement on decommissioning

He added: "We believe the context must effectively be changed by the British Prime Minister. He is the key."

Mr McGuinness said it was crucial to try to reach an agreement as soon as possible as the tensions of the marching season are returning.

He then called on the UK and Irish governments to reconvene talks on establishing the Northern Ireland executive to which Mr McGuinness and Bairbre de Brun have both been nominated as Sinn Fein's representatives.

The BBC's Laura Trevelyan: The window of opportunity is narrowing

Mr McGuinness also called for the head of the international body on decommissioning, General John de Chastelain, to assert himself publicly on the issue of paramilitary weapons.

UUP negotiator Sir Reg Empey emerged from the Stormont talks saying there was no sign of movement on the key unionist demand - decommissioning.

"During the weekend, the republican movement indicated that IRA decommissioning was undeliverable," said Sir Reg.

"Until this matter is resolved to the satisfaction of the parties, an executive is equally undeliverable."

Sir Reg also said that only the local parties could resolve the issue, clashing with Sinn Fein's calls for Mr Blair to move the process on.

Monday's meeting follows Sinn Fein's annual conference at the weekend and Downing Street talks between the two leaders last week.

Speaking to his party's members, Mr Adams called on Mr Blair and his Irish counterpart Bertie Ahern to force progress in the stalled peace process.

Momentum has faded in the talks after a series of deadlines passed without any advance towards the Northern Ireland Assembly taking up its powers.

The Ulster Unionists, led by Mr Trimble, refuse to sit in the assembly's executive, or cabinet, with Sinn Fein until the IRA begins decommissioning its arms.

Gerry Adams: Calling on the UK and Irish government to force progress

The republican party, which is entitled to two seats in the executive, maintains it cannot force the paramilitary group to start the process of destroying its weapons stockpiles.

It further points out that decommissioning was never a precondition to taking up ministerial seats in the Good Friday Agreement, which set out the basis for devolution in the province.

Mr Adams at the weekend repeated his demand on the UK and Irish governments to call the unionists' bluff and trigger the procedure known as d'Hondt, allowing the executive to be formed.