LONDON – Facebook announced Tuesday it was working on new ways to keep users from stumbling across gruesome content on its website following an outcry over the discovery of beheading videos there.

The controversy – which has drawn critical comment from British Prime Minister David Cameron – illustrates the difficulty of setting a universal standard across the social network used by 1 billion people.

Facing sharp criticism, Facebook Inc. issued a statement clarifying that violent videos were only allowed if they were presented as news or held up as atrocities to be condemned.

“If they were being celebrated, or the actions in them encouraged, our approach would be different,” the company said in a statement.

“However, since some people object to graphic video of this nature, we are working to give people additional control over the content they see. This may include warning them in advance that the image they are about to see contains graphic content.”

Facebook banned beheading videos in May but recently lifted the prohibition – a development flagged by the BBC on Monday. A few groups have since condemned the social network for potentially exposing users to the violent content.

Cameron, whose right-leaning government has unveiled several initiatives to censor objectionable content online, said Tuesday allowing the beheading videos back on Facebook was “irresponsible.”

Facebook’s administrators face constant pressure from interest groups trying to impose their own forms of censorship or fighting to lift restrictions they see as oppressive.

Violent news content poses particularly thorny questions for a website that allows children as young as 13 to join.