Three teenagers in the U.S. who allegedly raped a 12-year-old girl in December and posted the video of the crime on Facebook will be tried as adults. The boys were held in custody in lieu of the $900,000 [A$918,000] bail in a hearing before the criminal court on Friday.

Scandale Fritz, and Applewhite, both 16-year-olds, and 15-year-old Kenneth Brown of Cook County in Chicago, have been charged with raping the unnamed girl at gunpoint and posting the horrendous act on Facebook, the Chicago Tribune reported.

The act, as per police records, took place in Fritz's home on December 15 at 3:30 p.m. The girl went to the house to talk to Fritz, but when she went inside, she saw Brown with a gun in his pocket. Fritz then took her downstairs in the basement.

The prosecutors said that when she declined his demands for sex, Fritz raped and sodomised her. Brown and Applewhite also came downstairs, and Fritz ordered the girl to have sex with the other two boys. The girl initially refused, but saw Brown's gun. They sexually assaulted her and forced her to perform sex acts on them while Fritz filmed the scene.

All three boys are visible in the video, which also sees Brown holding a gun during the sexual act. They are heard shouting gang slogans.

The girl told someone about the attack the day after the incident. She was treated and examined at a hospital, and a police report was made.

The video was posted on Brown's Facebook page first on December 17, then on all the three boys' accounts.

Prosecutors told the paper that Fritz confessed to filming their crime.

Applewhite has no prior criminal records, while both Fritz and Brown have. They are due back in court on June 6 where they will be tried as adults.