Nigerian officials have ordered a boarding school closed and police are investigating a boy's allegations of brutal and repeated sexual assault.

Authorities in Nigeria's northern Kano city acted late Friday after a nurse refused to treat the child unless police were informed because of the gravity of his injuries, his mother told the Freedom Radio station.

She said her 11-year-old son complained his bottom was so sore he could not walk. She said the child told her he had been repeatedly raped in his dorm at night by an unknown person. Journalist Nasir Zango, who interviewed her, said he has since received death threats.

Officials of the Hassan Ibrahim Gwarzo College declined comment. Kano state set up a commission of inquiry and police confirmed they also are investigating.