Martin McGuiness says Gerry Adams is being deliberately targeted by those who are "maliciously and vehemently hostile to the peace process", after the Sinn Fein leader is detained by police.

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The deputy first minister said that Mr Adams could have been questioned without being arrested by detectives investigating the 1972 murder of Jean McConville.

Mr McGuiness also said that former Republicans and those who were "maliciously and vehemently" hostile to the police process were targeting the Sinn Fein leader, and added: "It has been disappointing to see the efforts of some of those people together in consort with the dark side within policing."

Prime Minister David Cameron has denied any political interference in the arrest, as did Northern Ireland first minister and the police ombudsman.

Mr McGuinness also said that senior members and "reformers" of the Police Service of Northern Ireland (PSNI) had told Sinn Fein about a "dark side" within the force, who had been conspiring with those intent on ruining the peace process. He added: "I think we have seen that dark side flex its muscles in the course of the last couple of days."

The killing of McConville, and the subsequent "disappearing" of her body until it was found 2003, is one of the most emotive murders from the Northern Ireland conflict.

No-one has ever been charged. But the veteran head of Sinn Fein has long been rumoured to have been involved, and Mr Adams was arrested by police on Wednesday night after voluntarily presenting himself for interview at a police station in Antrim.

He has once again rejected the allegations made by former republican colleagues that he had a role in ordering the notorious IRA killing in 1972.

Sinn Fein deputy leader Mary Lou McDonald said the arrest was "politically motivated" and designed to damage the party and its president.

Read more: Gary Gibbon blogs on the implications of Gerry Adams' arrest

After years without any progress in the criminal investigation there have been a series of arrests in recent weeks. Ivor Bell, the 77-year-old Republican, was charged in March this year with aiding and abetting the murder. Five other people have been detained and questioned.

The recent police activity has come in the wake of a decision by a court in the United States that compelled a university in Boston to hand over recorded interviews with republicans about McConville's murder, to the Police Service of Northern Ireland (PSNI).

Boston College has interviewed a number of former paramilitaries about their role in the Northern Ireland conflict, on the understanding transcripts would not be published until after their deaths.

But that pledge was effectively overturned when the court last year ordered that tapes that contained claims about the killing be given to detectives.

In the wake of the recent developments, Mr Adams, who has always denied membership of the IRA, said in March he would be available to meet with detectives if they wished to speak with him.

Below: Jean McConville's son Michael, who was 11 when she was abducted from the family home in front of him, says he knows who killed his mother, but is too scared of retribution to tell the police.

'I am innocent of any part in the killing of Mrs McConville'

Mr Adams, 65, a former MP for West Belfast and now a representative for Co Louth in the Irish Dail, presented himself at Antrim police station by prior arrangement with officers.

He issued a statement minutes after the PSNI announced an arrest had been made. "While I have concerns about the timing, I am voluntarily meeting with the PSNI this evening," he said last night, questioning why police chose to interview him in the run up to an election.

"As a republican leader I have never shirked my responsibility to build the peace. This includes dealing with the difficult issue of victims and their families. Insofar as it is possible I have worked to bring closure to victims and their families who have contacted me. Even though they may not agree, this includes the family of Jean McConville.

"I believe that the killing of Jean McConville and the secret burial of her body was wrong and a grievous injustice to her and her family. Well publicised, malicious allegations have been made against me. I reject these.

"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."

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