Northern Ireland’s Deputy First Minister Martin McGuinness has accused the police service of waging a political campaign over the arrest of Sinn Fein’s President Gerry Adams.

Adams handed himself in for questioning on Wednesday over the abduction and murder of Jean McConville, more than 40 years ago.

Adams’ deputy says a “dark side” within the police is to blame for his continued detention ahead of European and Irish elections.

“I view his arrest as a deliberate attempt to influence the outcome of the elections that are due to take place in three weeks’ time north and south on this island,” said McGuinness.

But Northern Ireland First Minister Peter Robinson dismissed the suggestion: “All I can say is that it strengthens our political process in Northern Ireland for people to know that no-one is above the law,” he said.

Britain’s Prime Minister David Cameron also rejected claims that Adams’ arrest is politically motivated: “We have an independent judicial system, both here in England and also we do have one in Northern Ireland, and there’s been absolutely no political interference in this issue,” he said.

Jean McConville, a mother of 10, was accused by the IRA of being an informer. She was abducted in front of her children, tortured, murdered and buried in secret for decades. Her body was found on a beach in County Louth in 2003.

Adams denies any role in her death or in the IRA.