The deadline for restoring powersharing in Northern Ireland runs out later today.
Sinn Fein has already said the three weeks of negotiations have run their course and they will not be nominating a deputy first minister in the devolved administration at Stormont.
Northern Ireland Secretary James Brokenshire could call new Assembly elections within a reasonable period or direct rule may be imposed from London once the 4pm cut-off for agreement between the five main Northern Ireland parties is reached.
The health system, policing and a range of other public services are facing major cuts if no budget is agreed for next year.
Powersharing collapsed in January after a row over a botched green energy scheme predicted to cost the taxpayer up to half a billion pounds.
Martin McGuinness resigned in protest over the Democratic Unionists handling of the scheme, triggering crisis in the institutions.
Sinn Fein has said it will not share power with the DUP leader Arlene Foster as first minister until a public inquiry into the renewable heat incentive (RHI) is concluded.
Republicans have also been seeking movement on issues like an Irish language act giving the tongue official status in Northern Ireland, a hugely symbolic measure but deeply problematic for some unionists.
They want to see progress on legacy funding for Northern Ireland conflict victims waiting up to 45 years for answers over how their loved ones died.
Mr Brokenshire chaired the talks in Belfast and said they had a duty to victims to address past violence which left 3,637 dead and countless more injured.
Sinn Fein have now called time on the current round of negotiations.
Its president Gerry Adams said thinking unionism was at a crossroads.
"The DUP cannot be in there representing the DUP voters.
"They have to work with us and any other party in there representing everyone.
"We don't have the basis for doing that, we are not going back to the status quo, but will we be back, will we get the institutions in place? Yes."
He said the terms did not exist now to nominate for a deputy first minister.
"That is today...we do believe that we will have the conditions in the time ahead because we want to be in the institutions."
He said unionists needed to help build a society that respected the rights of everyone.
"That is the big change that has come about and it is amplified in many ways by Martin McGuinness's term in office - you do it for everybody."
A voting surge by Sinn Fein in the last Assembly election earlier this month saw the party come within one seat of becoming the biggest party at Stormont behind the DUP.