Facebook is allowing videos showing people being decapitated to be posted and shared on its site once again.
The social network had introduced a temporary ban in May following complaints that the clips could cause long-term psychological damage.
The US firm confirmed it now believed its users should be free to watch and condemn such videos. It added it was, however, considering adding warnings.
One suicide prevention charity condemned the move.
"It only takes seconds of exposure to such graphic material to leave a permanent trace - particularly in a young person's mind," said Dr Arthur Cassidy, a former psychologist who runs a branch of the Yellow Ribbon Program in Northern Ireland.
"The more graphic and colourful the material is, the more psychologically destructive it becomes."
Two of the firm's official safety advisers have also criticised the decision.
Facebook allows anyone aged 13 and above to be a member.
Its terms and conditions now state that it will remove photos or videos that "glorify violence" in addition to other banned material, including a woman's "fully exposed breast".
The BBC was alerted to Facebook's change in policy by a reader who said the firm was refusing to remove a page showing a clip of a masked man killing a woman, which is believed to have been filmed in Mexico.
It was posted last week under the title, Challenge: Anybody can watch this video?
"Remove this video too many young innocent minds out there shouldn't see this!!!" wrote one user in the comments section below.
"This is absolutely horrible, distasteful and needs to be removed... there are too many young minds that can see this. I'm 23 and I'm very disturbed after seeing a couple of seconds of it," wrote another.
The social network later confirmed it was allowing such material to be posted again.
"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," said a spokeswoman.
"People are sharing this video on Facebook to condemn it. If the video were being celebrated, or the actions in it encouraged, our approach would be different.
"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."
The firm also disabled the adverts for third-party products that had been appearing alongside the video.
Facebook originally pulled decapitation videos after the Family Online Safety Institute - a member of its Safety Advisory Board - complained that they "crossed a line".
The charity's leader Stephen Balkam told the BBC he was surprised by the latest development.
"I would have expected a heads-up on this," he said.
"I went to have a look at the video and there's no warning label nor is there any condemnatory context. It's just sort of up there and the first image you are presented with is a woman's head being held by a guy.
"I'm very unhappy that these have gone back up and that they have gone up without any warning. First thing tomorrow morning I intend to raise this with Facebook."
Another of the board members, London-based Childnet International, said it also had concerns.
"Such content should be taken down," said its chief executive Will Gardner.
"There is a need to raise issues happening around the world, there is that argument, but some content is horrific.
"We would want to see steps to try and protect people from coming across such content. I'll tell Facebook what our view is, absolutely."
Decapitation videos are available elsewhere on the net but critics have raised concern that Facebook's news feeds and other sharing functions mean it is particularly adept at spreading such material.
"I have seen some of these videos - they are profoundly shocking," said John Carr, who sits on the executive board of the UK government's Council on Child Internet Safety.
"Facebook has taken leave of its senses. Those videos will fuel countless nightmares among the young and the sensitive."
Google's rival Google+ social network has a more restrictive policy: "Do not distribute depictions of graphic or gratuitous violence."
The idea of Facebook issuing a similar blanket ban had, however, concerned some freedom-of-speech campaigners who had suggested it was the responsibility of parents - not the company - to protect children on the internet.
However, the French digital rights group La Quadrature du Net said it was still concerned that Facebook was reserving the right to take down the videos if it took issue with the way they were presented.
"It shows how much Facebook is in power to decide whatever will or will not be expressed through its network," said the organisation's co-founder Jeremie Zimmermann.
"It plays a profoundly anti-democratic role when it makes any such choice, whatever the limits are and whatever the good reasons it uses to make the decision. Only a judicial authority should be able to restrict fundamental freedoms according to the rule of law."