An election in Northern Ireland looks inevitable after Sinn Féin refused to nominate a deputy first minister to replace Martin McGuinness.
He quit last week when DUP leader Arlene Foster refused to stand aside as first minister while a botched energy scheme was investigated.
Because they hold a joint office, the resignation automatically put the DUP leader out of her job.
Elections must be called if the positions are vacant for seven days.
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During Assembly proceedings on Monday, the Democratic Unionist Party (DUP) re-nominated Mrs Foster as first minister but Sinn Féin did not put forward a replacement for Mr McGuinness, meaning neither can resume their jobs at Stormont.
Assuming there is no last minute breakthrough by 17:00, the onus will be on Secretary of State James Brokenshire to name a date for a fresh election either in late February or early March.
Just ahead of the deadline, Sinn Féin said the party had been “stretched to the limit” by the DUP and it was “calling time” on the Stormont institutions.
Conor Murphy said the party would not return to the executive unless there was “fundamental change to the approach of the DUP and how they do power sharing”.
By BBC News NI political correspondent Gareth Gordon
If the Assembly – Nomination Day was a film, it would already have been declared a box office hit.
Stormont’s Great Hall crackled with atmosphere not seen since the distant days of David Trimble.
The problem was even before they took their front row seats, observers knew where this particular drama was going.
Sinn Féin issued enough spoilers. No, they would not be re-nominating for the position of deputy first minister and they were as good as their word.
The main player Martin McGuinness did not have to utter a single word. He delivered all the lines he needed to a week ago.
His resignation was the real drama.
Then we can get on with the sequel, Election Day – the Movie. If anyone tells you they know how that one will end don’t believe them.
Sinn Féin MLA Michelle O’Neill paid tribute to Mr McGuinness’s “Trojan efforts” during his 10 years as deputy first minister and said her party would not tolerate the “arrogance and disrespect of the DUP”.
“Sinn Féin will only be part of institutions which work and deliver for all in the community,” she said. “There can be no return to the status quo. If something is broken, you stop and you fix it.”
Speaking earlier, Mrs Foster said it was “deeply regrettable” that the Assembly would be dissolved in the next couple of days.
She said Northern Ireland did not need an election and Sinn Féin’s position “risks Northern Ireland’s future and stability and suits no-one but themselves”.
In other developments:
- Mr McGuinness tweeted that he had spoken to UK PM Theresa May and Mr Brokenshire on Monday morning
- Mrs May’s spokeswoman said the prime minister had also spoken to Mrs Foster to stress the importance of Northern Ireland having “a voice” in Brexit negotiations
- Sinn Féin leader Gerry Adams said there was an onus on the British and Irish governments to protect the institutions in Northern Ireland
- Sinn Féin’s motion of no confidence in DUP Speaker Robin Newton was vetoed by the DUP using a petition of concern, designed to safeguard minority rights and nicknamed the “joker card”
- DUP Communities Minister Paul Givan secured Assembly approval for the payment scheme for households set to lose out under the UK government’s so-called “bedroom tax”
- Some members of the economy committee held an emergency meeting on Monday morning, questioning Economy Minister Simon Hamilton and his most senior civil servant, Andrew McCormick, about RHI
As the business of Stormont continued, MLAs (Members of the Legislative Assembly) debated Mr Hamilton’s plan for cutting the cost of the subsidies paid to claimants under the controversial Renewable Heat Incentive (RHI) scheme.
The scheme is projected to run £490m over budget, although the DUP say their plan will eliminate the overspend.
An association representing the claimants has written to MLAs arguing that the proposed changes to the scheme could be overturned by a legal challenge.
Mrs Foster was the minister in charge of the RHI scheme when it was set up in 2012.
It was designed to encourage businesses to switch from fossil fuels to more environmentally friendly energy sources. But subsidies were overly generous and initially there was no cap on the payments.