Northern Ireland police have obtained a 48-hour extension to question detained Irish republican leader Gerry Adams over the notorious IRA murder of a widowed mother of 10 in 1972.

“Detectives investigating the abduction and murder of Jean McConville have been granted an extra 48 hours to interview a 65-year-old man,” a spokesman for the Police Service of Northern Ireland (PSNI) said on Friday.

Adams, 65, who is leader of the Sinn Fein political party and has been the public face of the movement to end British sovereignty in Northern Ireland for the past 30 years, presented himself at Antrim police station late on Wednesday.

Following two days of questioning, police were due to either release or charge him. But a judge has now ruled that Adams can be held until Sunday in a move likely to further enrage republicans.

Deputy First Minister Martin McGuinness, the senior Sinn Fein figure in the power-sharing government in Belfast, earlier said: “Yesterday I said that the timing of the arrest of Gerry Adams was politically motivated.

“Today’s decision by the PSNI to seek an extension to his detention absolutely confirms that view.”

Adams, who played a leading role in the peace process in the troubled British province, strongly denies involvement in the abduction and murder of Jean McConville.

The woman was snatched from her Belfast home in one of the most infamous cases of the three decades of sectarian conflict known as The Troubles.

She became one of 17 so-called “disappeared” until the Irish Republican Army (IRA) paramilitary group claimed her murder in 1999. Her body was found four years later.

McGuinness, a former IRA commander, said he expected Adams to be “totally and absolutely exonerated”.

But he warned that if Adams were charged, Sinn Fein might “review” its support for policing, which is fundamental to the success of the Northern Ireland government, where Catholic Irish nationalists share power with pro-British Protestants.

McGuinness accused the “dark side” of policing for conspiring with republican enemies of the peace process.

Northern Ireland Justice Minister David Ford, a member of the cross-community Alliance party, said there was “no evidence” of political policing.

British Prime Minister David Cameron called McGuinness on Thursday night to discuss the arrest of Adams.

Cameron also called First Minister Peter Robinson, leader of the Democratic Unionist Party (DUP), who has backed the arrest of Adams as proof that “no one is above the law”.