Police have raided the offices of Birmingham City as part of an investigation into corruption in football.

City of London Police visited the club early in the morning to execute a search warrant and left with financial documents, but did not give further details.

Birmingham said they are cooperating with police, but stressed the inquiries relate to a third party or parties unconnected to the club.

"For the avoidance of doubt, no one connected with the club has been questioned or arrested," the club said in an official statement.

Karren Brady, Birmingham's managing director, added: "We are co-operating fully with the police in their investigation, which is in connection with a third party."

Police have been investigating illegal payments relating to transfer activity in English football for the past two years, but so far made no convictions.

The highest profile arrest to date was that of Harry Redknapp, the Portsmouth manager, who was questioned by police and then released on bail last November.

In July, police searched the offices of Portsmouth, Newcastle United and Rangers and also questioned Pascal Chimbonda, the Tottenham Hotspur defender.