Facebook has refused to host ads from a US millionaire promoting gun training and offering $3m worth of free handguns.

Dr Ignatius Piazza, founder and director of Front Sight Firearms Training Institute, had submitted pay-per-click ads on Facebook offering a four-day handgun training course and a one-day concealed weapon permit course.

The ad also offered a free Springfield Armory XD handgun to the first 5,000 readers who responded.

Piazza said that he was left "stunned" when Facebook rejected his ad on the ground that it violated Point 6 of the social networking site's advertising guidelines.

"Provocative images will not be accepted. Ads may not contain, facilitate or promote adult content, including nudity, sexual terms and/or images of people in positions or activities that are excessively suggestive or sexual," Facebook's Point 6 states.

"Ads may not contain, facilitate or promote offensive, profane, vulgar, obscene, or inappropriate language. Ads may not contain, facilitate or promote defamatory, libellous, slanderous and/or unlawful content."

Piazza said in response: "Facebook administrators must find the idea of Front Sight positively changing the image of gun ownership through training law-abiding citizens in the safe and responsible use of handguns to be offensive, profane, vulgar and obscene.

"It appears to me that Facebook is discriminating against gun owners and placing gun ownership in the same category as pornography."