Updated

Officials in South Sudan say the U.N. has gathered evidence of gruesome attacks being carried out in the country's month-old conflict.

The officials say that some victims of ethnic-based attacks have been bound and others beheaded. Victims have also told The Associated Press that attackers have forced them to participate in sex acts with family members.

The U.N.'s assistant secretary-general for human rights, Ivan Simonoviae, is scheduled to give a news conference Friday. The two officials who detailed the violence insisted on anonymity because they weren't authorized to release the information.

Human Rights Watch, in a report Thursday, said the worst ethnic-based attack took place in mid-December, when 200 to 300 men from the Nuer ethnic group were jammed into a room that gunmen fired into, killing nearly everyone.