Martin McGuinness said progress needed to be made by Christmas
Stormont faces a "full-blown crisis" if Sinn Fein and the DUP do not resolve their differences before Christmas, Martin McGuinness has warned.
Northern Ireland's Sinn Fein deputy First Minister said there was a danger that the power-sharing arrangements would become "unsustainable".
The two parties have been arguing for months over the transfer of justice and policing powers from London to Belfast.
Sinn Fein wants it to happen now but the DUP says more confidence is needed.
In a BBC interview, Mr McGuinness said: "My approach to every difficult situation is to find a resolution, not to look for destruct buttons.
Mark Simpson, BBC Ireland correspondent
The current power-sharing arrangements at Stormont are facing their biggest test.
At stake is the future of devolution. The sticking point is when policing and justice powers should be transferred from London to Belfast.
Sinn Fein's Martin McGuinness has now effectively set a New Year deadline.
Although Northern Ireland's recent history is littered with missed deadlines, this one is not impossible.
Sinn Fein and the Democratic Unionists are still talking, and, crucially, they both want power-sharing to work.
However, the argument is not about power - it's about sharing.
This is where it gets tricky.
With a UK general election looming neither party wants to be seen giving ground. But without a new-found spirit of compromise, a deal cannot be done.
Like the Christmas decorations, the Stormont Assembly could be coming down in the new year.
"I have to say that if we don't get a date for transfer of power of policing and justice before Christmas to be effective in the new year, I do think we are in an unsustainable position.
"We would then be moving from what is a very serious situation into a full-blown crisis."
Mr McGuinness has made similar comments in recent days, but this is his most strongly-worded statement yet.
DUP MP Jeffrey Donaldson said Sinn Fein were engaging in "sabre-rattling".
"The DUP have made it clear that they're not going to be threatened or bullied by anyone.
"What is important is that we get the conditions right.
"Surely Sinn Fein know by now that setting arbitrary deadlines for anything in Northern Ireland is a recipe for not getting it done by the deadline."
The transfer of policing and justice powers is often referred to as the last piece of the devolution jigsaw.
DUP leader Peter Robinson has said it will only take place when there is sufficient community confidence.
The government has agreed a funding package thought to be in the region of £800m to fund the transfer.
The first and deputy first ministers have written to assembly members inviting them to nominate candidates for the post of justice minister by next week.
The letter from Mr Robinson and Mr McGuinness made it clear they will not pick one of their own party members, and the leader of the cross-community Alliance Party has been widely tipped to take the job.
Northern Ireland Secretary Shaun Woodward said he was still hopeful a deal would be reached shortly.
"Only yesterday (Thursday) the first minister and deputy first minister sent letters to all the other party leaders in Northern Ireland, asking them to nominate a justice minister; and of course this week, the Stormont Assembly completed the passage of a bill to create the new justice department," he said.
"Now we will now go on and get royal assent for that bill.
"So I see real progress being made here and I think that in the coming weeks it will be possible to achieve those last parts of the package that will allow devolution to go through for policing and justice."