Clashes erupted between Iranian police and members of a Sufi Muslim religious community in Tehran, leaving three officers dead, said the law enforcers.
A protest by dervishes at a police station in northern Tehran turned violent when the policemen were hit and killed by a bus.
Rights groups say Sufi dervishes have faced persecution in Iran.
One Iranian news agency described the incident as ‘deadly and bloody’ and the dervishes as a ‘cult’.
Nine protesters including the bus driver have been arrested, reports the BBC quoting an Iranian police spokesman.
Videos published on social media before the incident showed dervishes holding a sit-in protest in front of a police station against the detention of one of their members.
A video posted on Twitter shows some protesters marching in the middle of the road and some others sitting on the road, holding banners with the photo of the arrested dervish, chanting ‘God is great.’
Dervishes reported that the police used tear gas to disperse their gathering and videos on social media showed riot police chasing the protesters.