Stormont Assembly election will take place on March 2, the Northern Ireland Secretary has announced.
James Brokenshire called the poll minutes after a deadline elapsed that effectively triggered the collapse of the powersharing executive in Belfast.
Mr Brokenshire was obliged by law to set an election date after Sinn Fein brought down the institutions by refusing to replace Martin McGuinness as deputy first minister.
Mr McGuinness quit last week citing irreconcilable differences with his long-term Democratic Unionist partners in government.
The deadline for Sinn Fein to re-nominate a minister passed at 5pm on Monday.
Mr Brokenshire said: "No one should underestimate the challenge faced to the political institutions here in Northern Ireland and what is at stake.
"While it is inevitable that debate during an election period will be intense, I would strongly encourage the political parties to conduct this election with a view to the future of Northern Ireland and re-establishing a partnership government at the earliest opportunity after that poll.
"The Government continues to stand firmly behind its commitment to the Belfast Agreement and its successors, and our responsibilities to safeguard political stability.
"We will continue to do all that we can to find a way forward and secure the continuation of devolved government and I will make a further statement in Parliament tomorrow."
Mr McGuinness's resignation was precipitated by the renewable heat incentive (RHI) scandal - a botched eco-scheme set to cost Stormont £490 million - but that row has also reignited a range of other bitter disputes dividing the coalition.
Sinn Fein MLA Michelle O'Neill told the Assembly: "The DUP have treated these institutions and sections of the community with contempt and arrogance.
"Today, Sinn Fein will not re-nominate for the position of deputy first minister."
Ms O'Neill said Sinn Fein would only return to government if there was "real and meaningful change".
Mr McGuinness's resignation automatically removed DUP leader Arlene Foster from her position as first minister - as executive structures dictate one cannot govern without the other.
On Monday, the DUP renominated Mrs Foster to the post. That was rendered meaningless by Sinn Fein's subsequent refusal to renominate its own incumbent at the head of the executive.
Mrs Foster claimed the electorate did not want or need an election.
She accused Sinn Fein of triggering a poll because they did not like the outcome of last May's vote.
"They have forced an election that risks Northern Ireland's future and stability, and which suits nobody but themselves," she said.
Theresa May phoned Mrs Foster and Mr McGuinness early on Monday in a last-ditch effort to prevent the collapse of the devolved administration. But her intervention was to no avail.
The Stormont Assembly will limp on until it is formally dissolved next week, when the election campaign will begin in earnest.
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