The UUP has indicated it may not attend a fresh round of talks aimed at saving power-sharing at Stormont.
The discussions were called for on Thursday by the governments of both the UK and the Republic of Ireland.
A statement from No 10 Downing Street said talks should be “intensive”, “urgent”, and should include all parties which had helped negotiate the Stormont House Agreement in 2014 – namely the Alliance, DUP, UUP, SDLP and Sinn Fein.
The DUP said they “welcome the announcement of talks as a first step”, and a spokesman suggested discussions could get underway early next week.
In the face of the demands for rapid engagement from both London and Dublin, senior UUP figure Reg Empey yesterday said they had not made up their minds about taking part.
He said: “Mike Nesbitt said he wants to see the terms and conditions of these talks before he makes up his mind.
“We need to see what the details are and he’ll be eager to see what that amounts to before he makes any decision.”
He added: “The Secretary of State would have to tell the invitees what the process is, what the agenda is...
“There are no guarantees [we will take part]. And how can you give a guarantee when you haven’t actually heard the terms of reference?”
Asked what the chances would be of implementing any agreement made in the absence of the UUP, he said: “I’m not getting into that sort of speculation.”
This will now be the third year that Northern Ireland’s main parties are set to enter into a major talks process – something which has failed on the past two consecutive occasions.
Lord Empey said it reflected “years of underperformance by the Assembly”.
“Most people are horrified by it; embarrassed by it; ashamed of it, in many respects,” he said.
“I think it’s terribly disappointing and very frustrating that we’re back again where we started – and I do think that is a shame. However, we’ll go along, see what happens, and Mike will make his mind up.”
The Northern Ireland Office could not be reached last night.