Ken Livingstone has refused to say sorry for comparing a Jewish newspaper reporter to a concentration camp guard.

Despite pleas from Labour colleagues, London's mayor said he could not withdraw remarks he made to a London Evening Standard journalist because to do so would make him a "liar".

The Board of Deputies of British Jews has formally reported Livingstone for investigation by the local government watchdog, accusing him of "gross insensitivity" and potentially threatening him with suspension.

The mayor said he had been the victim of a 24-year hate campaign by Associated Newspapers, publishers of the Evening Standard, and the Daily Mail.

He told London assembly members: "If I could in anything I say relieve any pain anyone feels I would not hesitate to do it, but it would require me to be a liar.

"I could apologise but why should I say words I do not believe in my heart? Therefore I cannot. If that is something people find they cannot accept, I am sorry, but this is how I feel after nearly a quarter of a century of their behaviour and tactics."

He added: "The comments I made simply indicated the level of loathing and disgust for the racism they have perpetuated and the bigotry they have encouraged for over 100 years."

Executives at the Evening Standard denied being part of  hate campaign against the mayor.

"We supported him in the mayoral election last year but in this case we feel he fell far short of what is expected of a figure in his position and he has caused great offence," a statement said.