Sinn Fein has said the talks process aimed at restoring devolution in Northern Ireland has run its course.
The republican party will not be nominating a deputy first minister on Monday, leader at Stormont Michelle O'Neill said, triggering another crisis at Stormont.
However President Gerry Adams said he believed the conditions to go back into power-sharing would be achieved in the time ahead.
Mrs O'Neill said: "Today we have come to the end of the road."
Monday is the deadline for nominating a first and deputy first minister at Stormont or else Northern Ireland Secretary James Brokenshire is obliged to intervene.
Fresh elections or direct rule from Westminster could be imposed within a reasonable period.
Mrs O'Neill added: "The talks process has run its course and Sinn Fein will not be nominating for the position of speaker or for the executive office tomorrow."
Power-sharing collapsed in January after a row over a botched green energy scheme predicted to cost the taxpayer up to half a billion pounds.
Sinn Fein has said it will not share power with the Democratic Unionists' 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 also 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 is chairing talks in Belfast and said they had a duty to victims to address past violence which left 3,637 dead and countless more injured.
The five main parties only had until 4pm on Monday to resolve their differences or face another snap election.
Sinn Fein have now called time on the current round of negotiations.
Mr 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.
Irish foreign affairs minister Charlie Flanagan said: "Despite constructive engagement by all of the parties and important progress being made during these discussions, it has not yet been possible to make the necessary breakthroughs on a small number of core issues."
He said it was a critical time for Northern Ireland ahead of next week's triggering of Article 50 by the UK government.
"It is the strong wish of the Irish Government to see power-sharing re-established so that the interests of the people in Northern Ireland are best protected and advanced.
"I therefore urge the parties to avail of the remaining time available to re-engage on the few outstanding issues that divide them."
Nationalist SDLP leader Colum Eastwood blamed the impasse on an unwillingness to find creative compromise on key elements of former agreements.
He called on Mr Brokenshire to create space immediately for a reconvened and refreshed talks process.
He said: "Following talks over the last number of days it is clear now that an agreement will not be reached in the time left. That is a bitter disappointment.
"The clear message from the public after this month's election was an extreme frustration with the way government worked. After weeks of talks, the DUP clearly hasn't got that message.
"This wasn't just about RHI, it was about the way people and communities were treated, it was about a respect deficit, it was about an absence of equality.
"Those who are responsible for creating that poisoned political atmosphere must address it in word and action."
Ulster Unionist negotiator Tom Elliott said Northern Ireland could be in for a period of "prolonged drift" unless there is a massive u-turn in attitude from the DUP and Sinn Fein and said there was no recent roundtable discussion between all five parties.
"It was a clear indication that the bigger parties are even more dismissive of the smaller ones than ever, and demonstrates their inability to move away from their old ways.
"We have engaged in every set of recent negotiations from Haass O'Sullivan to today. This was simply the worst."