The plug will finally be pulled on the Stormont Assembly if a working administration is not formed in Belfast by the end of March, the British and Irish governments have warned.
Bertie Ahern, the Irish Premier, and Ulster Secretary Peter Hain issued the ultimatum to Sinn Fein and the Democratic Unionists amid continued political wrangling.
With republican endorsement of policing putting pressure on the DUP to pledge to share power, fresh elections in Northern Ireland are set for March 7.
But Mr Ahern and Mr Hain, who held talks in Cardiff ahead of the Six Nations Rugby clash between Wales and Ireland, insisted the deadline for establishing a coalition would not be extended.
In a joint statement, London and Dublin said: "The election on March 7 must be about the future of Northern Ireland, and that future lies in a locally accountable, devolved power-sharing Assembly and Executive. This must be in place on March 26. It is devolution or dissolution.
"There is no future in basing a political strategy on trying to delay devolution past March 26, or trying to prevent it altogether. Anyone who does will be left behind."
Earlier, Mr Hain stressed that Sinn Fein's decision to back the police in Northern Ireland had left Ian Paisley's DUP with no excuse to balk at power-sharing.
He said unionists were under no illusions that the governments were serious the cut-off point for getting Stormont up and running again.
"There have been a few off-stage noises recently where some politicians appear to be oblivious to that fact or are in denial. What has happened in the last week with Sinn-Fein's decision to get involved in policing at its special ard fheis (party conference) last week, and the remarkable series of statements by Gerry Adams afterwards, urging people in republican communities to cooperate with the police and encouraging them to join means Sinn Fein are well on their way to delivering what their leadership promised to do.
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"That was to comply with policing and the rule of law. That leaves no excuses for unionists to balk at power-sharing during the election or after that."
