An Afghan police chief says seven suspects have been arrested after a Kabul mob beat a woman to death, then set her body on fire and threw it into the Kabul River.

The city's head of criminal investigation, Mohammad Farid Afzali, said on Friday that the attack happened the previous night. He says the motive for the brutal assault was unknown.

Afzali says police "tried to disperse the crowd by shooting in the air, but reacted too late."

Cell phone footage has surfaced in the Afghan capital of the horrific beating. Afzali says the woman was known to have been under psychiatric treatment for the past four years.

Violence against women is endemic in Afghanistan but mob assaults on women in Kabul are extremely rare.