Gwent Police said they believe the incident was not a terrorist threat, but a hacking stunt.

The image, of a massacre of Palestinians which happened 22 years ago, appeared on the site on Sunday.

Police were alerted by a member of the public, but when officers logged on, it had been removed. An investigation has been launched.

Chief Superintendent Ray Wise said: "We are inquiring into this matter and are satisfied that there is no risk to the public.

"It would appear we are dealing with an individual hacking into an internet site and not dealing with any terrorist threat to person or property in this country."