BELFAST (REUTERS) - Northern Ireland's first minister denied any political motivation behind the arrest of Sinn Fein leader Gerry Adams who is being questioned as part of an investigation into one of the province's most notorious murders.

"Is anybody going to say to me that if the police are aware of claims and evidence in relation to such a barbaric killing that it would be political policing for them to question those who have been suggested to have been involved?" Peter Robinson asked reporters.

"I would suggest to you that it would be political policing if the PSNI had not questioned those that were deemed to have been involved in any way," Robinson said.

Northern Ireland's Deputy First Minister Martin McGuinness said the arrest of Adams was a deliberate attempt by unidentified "dark" forces within the Police Service of Northern Ireland (PSNI) to undermine the peace process and said it was linked to elections later this month.