Three police officers were killed in Tehran on Monday, a police spokesman said, as clashes broke out with members of a Muslim religious order seen as a threat to the Shi'ite theocratic establishment.
According to Fars News Agency, "an angry dervish bus driver ran over a group of policemen and created a carnage".
Often described as Islamic mysticism, Sufism emphasises the inner search for God and the renunciation of worldly matters.
Video footage posted on social media on Monday evening showed clashes between security forces and members of the Gonabadi Dervishes, an order following the mystical Sufi strain of Islam.
WATCH: Another video posted shortly afterward shows a auto plowing through security forces, reportedly leaving one Basiji dead.
Three policemen are reported dead and in addition a senior commander of Iran Basij militia force says two members of this force have also been killed in the clashes and at least one protester is dead.
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Ten of the protesters are also injured in the attack.
The protesters were dervishes from the Sufi order of Gonabadi.
Police forces fired air shots and tear gas to disperse the crowd, according to official IRNA news agency.
The Sufi protests began after the arrest of a person named Nematollah Riahi about two weeks ago during violence in northern Tehran, where the Sufis gathered outside the house of their guide, "Nurallah Tabenda", following reports that the security forces intend to arrest him.
The late U.N. Special Rapporteur on Human Rights in Iran voiced concern in 2017 about the "targeting and harsh treatment" of members of various Sufi groups, including the Gonabadi order and the Yarsan, also known Ahl-e Haqq.
It said members of the Gonabadi group continue to face abuses, including attacks on their prayer centers, destruction of community cemeteries, harassment, arrests, and physical assaults on their leaders.
In March 2017, the United Nations special rapporteur for Iran expressed concern over the state targeting of members of Sufi groups, saying they "continue to face arbitrary arrest, harassment, and detention and are often accused of national security crimes".