The Ulster Unionist party has walked out of crunch talks at Stormont, aimed at averting a collapse of the Northern Irish Assembly.
Leader Mike Nesbitt says his party will only engage in the talks if the existence of the IRA is the first point of order.
Ulster Unionist Party leader Mike Nesbitt (right) and MLA Michael McGimpsey speak to reporters outside Stormont in Belfast as they arrive for negotiations on the future of the power-sharing administration in Northern Ireland.
He has already led the party out of the power sharing executive amid claims provisional IRA members were involved in Kevin McGuigans murder last month.
Minister for Foreign Affairs Charlie Flanagan is co-chairing the negotiations with the Northern Ireland Secretary.
Mr Nesbitt is adamant the IRA must be the first item discussed: "They want to discuss implementation of the Stormont House Agreement tomorrow.
“We will not be there,” he said.
The intensive talks were launched after revelations the IRA still existed and members shot a man dead in Belfast last month.
Mr Nesbitt said: “This is the issue and the only issue that we will speak on.
“We will consider going into the session which deals with the IRA. We will consider it but we need to see the papers and the terms of engagement.
“That is what we said about going into these talks. Who would be there, what are the terms of engagement and what is the agenda?
“The fact that no other party supported us and said ’let’s change this proposed agenda, forget the Stormont House Agreement until we resolve the issue of Sinn Fein being in denial about the IRA’ is frankly appalling.”
The ministerial Executive at Stormont has been under threat of collapse since police said IRA members were involved in the murder of Kevin McGuigan in east Belfast last month.
Police believe Mr McGuigan was killed by individual members of the Provisional IRA in revenge for the death of prominent republican Gerard “Jock” Davison in May.
Although Police Service of Northern Ireland (PSNI) Chief Constable George Hamilton has insisted the IRA is not back on a war footing, disclosure that the organisation still exists has rocked the political establishment.
First Minister Peter Robinson said: “If the Assembly and Executive falls we are probably talking about the best part of a decade before it would ever be revived.
“These are extremely important talks. We enter it in a very serious manner.”
Meanwhile the North's First Minister Peter Robinson says concerns over paramilitary activities need to be resolved as part of the current talks.
Speaking on his way out of Stormont this evening Mr Robinson said there could be no agreement otherwise: "The issues that have to be dealt with, all have to be dealt with before anything is agreed by us.
"If the issue of the paramilitary involvement is not resolved then there will be no overall agreement."