ANTRIM (AFP) - The British and Irish governments denied on Thursday that the arrest of republican leader Gerry Adams was 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 on Wednesday night over the killing of mother-of-10 Jean McConville in 1972.

Mr 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," Mr Adams said.

Police must charge or release him by Friday night.

Ms 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, 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.

The arrest was a "deliberate attempt to influence the outcome of the elections in three weeks time", said Mr McGuinness.

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".

A police spokesman insisted they would "conduct a thorough and professional investigation...subject to the full rigours of scrutiny provided in the criminal justice system."

The US State Department, which was closely involved in brokering the peace agreement, said it hoped the arrest would not "impact the situation on the ground and we urge everyone to remain calm".