Pirated copies of the anti-Bush documentary "Fahrenheit 9/11" have become a best-seller in Kuwait despite an official ban by the staunch U.S. ally.

Vendors of bootleg DVDs say the movie has become popular in the tiny Gulf Arab country that is still publicly grateful to Washington - and former President George Bush - for liberating it from Iraqi occupation.

"This documentary is a favourite," said one Kuwaiti street vendor who was selling illegal copies sell for $3.40.

"The ban has only brought me more customers. We always want what we're not allowed to have," another vendor said.

Kuwait banned the film, saying it was "unfairly" critical of Gulf political heavyweight Saudi Arabia and the administration of President George W. Bush, which led the 2003 war that toppled Iraqi president Saddam Hussein.

Bush's father led the 1991 war that ended Iraq's occupation of Kuwait.

Saudi Arabia, which does not have any cinemas, has criticised the documentary, but it is being screened in packed theatres in other Gulf Arab states such as the United Arab Emirates and Bahrain.