PM calls Facebook irresponsible for allowing beheading clips

Facebook introduced a temporary ban on beheading videos in May but has since decided to remove the block. Photograph: Dave Thompson/PA

David Cameron has waded into the row over Facebook's decision to allow a video of a beheading to appear on its site, branding it "irresponsible" and saying the social networking site should explain it to "worried parents".

The prime minister tweeted that Facebook should put up a warning about the video – a move that sources close to the company say it is considering.

The row blew up after the company went back on a ban imposed in May on the posting of footage showing such killings. It said that it was only allowing the present video – which shows a masked man killing a woman in Mexico – because people were sharing the video to condemn it.

Yet Facebook's rules, under "nudity and pornography", would ban the display of topless photos.

Stephen Balkam, a member of the Facebook safety advisory board, urged the company to rethink the change in its policy. He told Sky News: "They have some very strict rules about nudity, about sex and even about violence, too. I just think in this case they really need to rethink how they use and how they adopt their own policies."

Facebook has said users should be free to view such videos and then condemn the content – and that it would take a different approach if the actions in the footage were "encouraged or celebrated".

Sources close to Facebook have indicated that the company is keeping its policies under close review as the furore over the posting of the video grew.

While it does have a "Like" button, to indicate approval, Facebook doesn't have any clear way for users to indicate dislike of content – meaning that it is hard for outsiders to know how the company could measure the basis on which people are viewing a video.

A Facebook spokeswoman said: "Facebook has long been a place where people turn to share their experiences, particularly when they're connected to controversial events on the ground, such as human rights abuses, acts of terrorism and other violent events."