BELFAST, Northern Ireland — Northern Ireland police were granted an extra 48 hours Friday to interrogate Sinn Fein leader Gerry Adams about the 1972 IRA killing of a Belfast widow, infuriating his Irish nationalist party and raising questions about the stability of the province's Catholic-Protestant government.

The Police Service of Northern Ireland confirmed in a statement its detectives received permission at a closed-door hearing with a judge to detain Adams for up to two more days.

Had the request been refused, authorities would have been required to charge Adams or release him Friday night, two days after his arrest in the abduction, slaying and secret burial of Jean McConville, a mother of 10. The new deadline is Sunday night, although this too could be extended with judicial permission.

The unexpectedly long detention of Adams left senior party colleagues seething. Sinn Fein warned it could end its support for law and order in Northern Ireland — a key peacemaking commitment that enabled the creation of a unity government seven years ago — if Adams is charged.

Deputy First Minister Martin McGuinness, the Sinn Fein official who governs Northern Ireland alongside British Protestant politicians, said his party would reconsider its 2007 vote to recognize the legitimacy of Northern Ireland's police if Adams isn't freed without charge. Protestants required that commitment before agreeing to cooperate with Sinn Fein.

McGuinness, who like Adams reputedly was an Irish Republican Army commander for three decades, said Sinn Fein would "continue to support the reformers within policing" if Adams is freed.

"Or the situation will not work out in the way we believe that it should. If it doesn't, we will have to review that situation," he said.

Moderate politicians criticized Sinn Fein for making unreasonable threats.

The justice minister in Northern Ireland's five-party government, David Ford, told journalists outside the police station where Adams was being held that detectives were just doing their jobs in investigating one of the most heinous crimes of the conflict. Without specifying any of his government colleagues, Ford said some were seeking to promote instability.

"I have seen no evidence, in the four years that I have been minister, of policing being operated on a political basis. I have certainly seen plenty of evidence of politicians from different backgrounds seeking to interfere in policing," said Ford, who leads Alliance, the only party actively seeking support from both the Irish Catholic and British Protestant sides of the divide. It receives few votes.

Were Sinn Fein to withdraw its support for law and order, it would offer a green light to today's still-active IRA factions to increase attacks on police. It also would risk the Protestant side's withdrawal from the power-sharing government, which in turn would force the Northern Ireland Assembly to be dissolved for an emergency election.

Adams, who as Sinn Fein chief since 1983 is Europe's longest-serving party leader, denies any role in the IRA. But IRA veterans who spoke on tape to a Boston College-commissioned oral history project say he was the outlawed group's Belfast commander in 1972 and ordered the killing and secret burial of McConville, whom the IRA branded a British army spy.

McConville's eldest daughter, who has led a two-decade campaign for the truth, says she's praying for a murder charge — and is prepared to name publicly those IRA members she believes stormed into their home on the day of her mother's abduction. Her other siblings say they're too afraid to take this step because it could inspire IRA attacks on themselves or their children.

"What are they going to do to me? They have done so much to me in the last 42 years. Are they going to come and put a bullet in my head? Well, they know where I live," Helen McKendry said.

The underground army killed nearly 1,800 people — including scores of Catholic civilians and IRA members branded spies and informers — before calling a 1997 cease-fire so Sinn Fein could pursue peace with Britain and Northern Ireland's Protestant majority.

Adams initially insisted in brief face-to-face meetings with McKendry that the IRA wasn't involved, but pledged to look into it. Finally in 1999, the IRA admitted responsibility for the slayings of nine long-vanished civilians and IRA members, including McConville, and offered to pinpoint her unmarked grave on a beach 60 miles (100 kilometers) south of Belfast in the Republic of Ireland.

That effort failed despite extensive digging. Then in 2003, a dog walker stumbled across her skeletal remains, with its bullet-shattered skull, protruding from a bluff above a different beach.

The police investigation of the McConville killing has accelerated since detectives last year won access to some of the Boston College tapes. Subjects agreed to speak candidly about their IRA careers on condition the interviews would remain under lock and key until their deaths, but the Northern Ireland police sued for access to all of them after one interviewee, Brendan Hughes, died and his accusations against Adams were published and broadcast in 2010.

Boston College successfully fought to limit the handover to 11 interviews from some half-dozen IRA figures who explicitly mentioned the McConville killing. It isn't known whether any others back Hughes' central accusation that Adams ordered McConville's body dumped in an unmarked grave rather than put on public display in Belfast, as other IRA leaders wanted.

While Sinn Fein has protested that Adams' arrest is politically biased, Northern Ireland's main newspaper wrote Friday that it suggested the opposite: that the police are unwilling to treat any politician as untouchable.

"The wheels of justice in his case must grind at exactly the same speed as those of anyone else questioned about a crime," the Belfast Telegraph wrote in its lead editorial.

"We have an independent police force and an independent prosecution service and we must trust them to act justly and according to the evidence before them," it said. "That is how a mature democracy treats its citizens, unlike the kangaroo court that sentenced Mrs. McConville to death."