The British and Irish governments have denied that the arrest of republican leader Gerry Adams is politically motivated, as Northern Ireland police questioned him over a notorious IRA murder.
The Sinn Fein president, who played a leading role in the peace process in the troubled British province, was arrested yesterday over the killing of mother-of-10 Jean McConville in 1972.
Adams, 65, strongly denied involvement in one of the most infamous incidents of the so-called Troubles in Northern Ireland and questioned the timing of the arrest before local and European elections.
"While I have never disassociated myself from the IRA and I never will, I am innocent of any part in the abduction, killing or burial of Mrs McConville," Adams said.
Police must charge or release him by Friday night.
McConville, 37, was snatched from her home in west Belfast in front of her screaming children, becoming one of more than a dozen so-called "disappeared" of the conflict.
Her body was found on a beach, shot in the back of the head, in 2003.
Sinn Fein was once the political arm of the Irish Republican Army (IRA), the now disbanded paramilitary group which waged a bloody campaign over three decades for Northern Ireland to become part of Ireland.
The party now shares power with its old foe, the pro-British Democratic Unionist Party (DUP), in a devolved government in Belfast and Sinn Fein member Martin McGuinness is deputy first minister.
McGuinness, a former IRA commander, accused a section of the police of trying to undermine the party with the "malicious" allegations and said the arrest was a "deliberate attempt to influence the outcome of the elections in three weeks time."
The British and Irish governments, which worked together on the 1998 Good Friday peace accords that largely ended the violence, tried to calm rising tensions.
"There has been absolutely no political interference in this issue," British Prime Minister David Cameron said.
His Irish counterpart, Enda Kenny, added: "All I can say is that I hope the president of Sinn Fein answers in the best way he can, to the fullest extent that he can, questions that are being asked about a live murder investigation."
Northern Ireland First Minister Peter Robinson, leader of the DUP, said the arrest proved that "no one is above the law".
"It would be political policing if the police had information and didn't follow it up because of the political profile of an individual," Robinson said.
The IRA had wrongly accused McConville of being an informer for the British army, but finally admitted her murder in 1999.
Her son Michael, who was 11 years old when he watched his mother being dragged away, said he was pleased the police were "doing their job", but admitted in a BBC interview that he still refused to name the people he saw, saying he still feared reprisals.
Nobody has been convicted of McConville's murder.