Facebook has confirmed it has begun placing clickable warnings over extreme "graphic" content on its service in order to prevent offence.
The notices placed over flagged images and videos - including those showing the death of French policeman Ahmed Merabet being shot dead in Paris - state that the content might "shock offend and upset".
"Are you sure you want to see this?" it asks. Videos with the warning will not autoplay like other newsfeed items, and cannot be seen by users who say they are under 18.
The move comes after safety advisers at the site and elsewhere said Facebook needed to impose greater controls on disturbing images, and who sees them.
"A photo or video containing graphic content may appear with a warning to let people know about the content before they view it, and may only be visible to people older than 18," Facebook said.
Facebook has long faced criticism for what has been called an overly complex response to graphic or disturbing content.
It carried out an experiment in 2013 to place warnings over graphic clips of beheadings, which was not rolled out across the entire site.
After a review, Facebook said at the time that it would not allow graphic content which glorified violence, but would not restrict those images if used to condemn or if it was in the public interest:
"Facebook has long been a place where people turn to share their experiences and raise awareness about issues important to them. Sometimes, those experiences and issues involve graphic content that is of public interest or concern, such as human rights abuses or acts of terrorism. In many instances, when people share this type of content, it is to condemn it. However, graphic images shared for sadistic effect or to celebrate or glorify violence have no place on our site.
When people share any content, we expect that they will share in a responsible manner. That includes choosing carefully the audience for the content. For graphic videos, people should warn their audience about the nature of the content in the video so that their audience can make an informed choice about whether to watch it."
But now Facebook says that beginning in December it will be placing warnings on material which users flag as graphic or as having been posted irresponsibly -- though presumably whoever sees it first won't have that benefit.
"When people share things on Facebook, we expect that they will share it responsibly, including choosing who will see that content," a spokeswoman told the BBC.
"We also ask that people warn their audience about what they are about to see if it includes graphic violence. In instances when people report graphic content to us that should include warnings or is not appropriate for people under the age of 18, we may add a warning for adults and prevent young people from viewing the content."