At least five Iranian security forces were killed in separate car-ramming attacks and a stabbing, blamed on Sufi Muslim followers who had been protesting alleged religious repression by the government in Tehran.
Three police officers were killed and several wounded in the first incident on Monday evening, when a minibus ran them over as they tried to contain the Gonabadi Dervish protesters in the Pasdaran district of the capital, Iran's Fars news agency reported on Tuesday.
A Gonabadi Dervish member drove the vehicle involved in the attack, it said. Al Jazeera could not independently verify the information.
One video clip posted on social media showed a white minibus speeding down a busy Tehran street, as dozens of police officers carrying batons and riot shields gave chase, with onlookers screaming.
In a separate incident, a member of the government-aligned Basij volunteer militia group was reportedly rammed by a car and another stabbed to death, according to Press TV.
The militia frequently patrols the streets of Iran, receiving direct orders from the Revolutionary Guard and Supreme Leader Ayatollah Ali Khamenei.
Press TV reported as many as 30 security forces and protesters were also injured during clashes.
Images posted by a Gonabadi Dervish-affiliated social media account showed several male members of the group with bloodied faces and foreheads, following apparent police beatings.
Another photo showed several people blocking a street and burning objects to prevent police from moving forward. There were also reports of torched vehicles and other damage to private property.
Tasnim news agency reported as many as 300 people have been arrested.
General Saeed Montazer al-Mahdi, a police spokesman, was quoted by Press TV as saying security forces managed "to restore calm and order" on Tuesday.
Video clips posted Tuesday on social media, however, showed police engaged in running battles with demonstrators on residential streets in Tehran's northern district.
Members of the Gonabadi Dervish religious order protested on Monday following reports that its ageing leader, Noor Ali Tabandeh, may be imprisoned by authorities.
As of Tuesday, there were no reports that Tabandeh, 90, had been arrested. The social media account Majzooban said several supporters of the religious leader were rounded up by authorities.
For years, members of the Gonabadi Dervish have complained of religious persecution and frequent imprisonments.
According to the Center for Human Rights in Iran, the Sufi Muslims are viewed as a threat to mainstream Shia Islam in the country, and its religious establishment frowns upon conversions.
In January, at least 10 members of the group were imprisoned in southern Fars province. Other followers are reportedly held at Tehran's Evin Prison.
For centuries, however, Iran has allowed other major religions - such as Christianity, Judaism and Buddhism - to exist in the country.