Iranian "morality police" were forced to fire warning shots when a crowd intervened to prevent them from arresting two women for not wearing a hijab.

The incident occurred in Tehran's northeastern Narmak neighbourhood on Friday night, and ended with a mob tearing the door off a police vehicle, Iran's state-run IRNA news agency reported.

"Morality patrol police members had warned two young women who did not have proper hijab. Within a few minutes, a group of citizens gathered around to prevent the transfer of the two women [into custody]," a police official told the agency.