Three men have been arrested following reports that a woman was gang-raped in an attack in Sweden that was streamed on Facebook Live.

The alleged assault took place in a flat in the town of Uppsala, north of Stockholm on Saturday (21 January).

Eye-witness Josefine Lundgren, 21, said she unwittingly viewed the live stream on a closed Facebook group and alerted police. She described seeing the victim being stripped and then sexually assaulted by a number of armed men in an attack that lasted several hours.

She told Sweden's Expressen newspaper: "He pulled her clothes off and lay on top of her."

She said the harrowing assault ended when police arrived and switched off the webcam.

Another online witness told the paper: "At first I thought it was a poorly orchestrated joke. The first thing you think is: 'How can you do such a thing to a girl? And how can you do it live?' It is totally sick."

According to Mail Online three men are being questioned by police while forensic scientists are investigating the apartment. The woman is said to be recovering from her ordeal in hospital.

It's the latest controversy for Facebook Live, after a Chicago man with learning difficulties was tortured online earlier this month.

Four suspects have been charged in connection with that kidnap and torture of a mentally disabled teenager that was broadcast on Facebook Live. The victim, 18, was shown being beaten, stripped, taunted, threatened with a knife and forced to drink from a toilet bowl during the ordeal in Chicago.

And in June last year gang member Antonio Perkins, 28, unwittingly live streamed his own death on Facebook after he was shot dead in Chicago while using the Real Time video app.The video of the shooting was watched more than 700,000 times.