Activists on Sunday expressed alarm that Iran was implementing a major crackdown in a Kurdish-populated town that has seen intense anti-regime protests in the last few days.
Reinforcements of the security forces were sent to the city of Mahabad in western Iran, rights groups said, while images and audio files of heavy gunfire and screams were posted overnight.
Iran's clerical leadership has been shaken by more than two months of protests sparked by the death in custody of Mahsa Amini, a 22-year-old woman of Kurdish origin who had been arrested by the Tehran morality police.
The very first protests took place in Kurdish-populated areas of Iran including at Amini's funeral in her home town of Saqez, before spreading nationwide.
Rights groups had earlier posted footage of defiant protests in Mahabad, including after the funerals of victims of the state's crackdown on the protests, with people staging sit-ins in the streets and setting up barricades.
The Norway-based Hengaw rights group said "armed troops" had been despatched to Mahabad from Urmia, the main city of West Azerbaijan province.
"In Mahabad's residential areas, there is a lot of gunfire," it wrote on Twitter.
The Iran Human Rights (IHR) group, also Norway based, posted footage overnight Saturday-Sunday that it said showed gunfire echoing around the city.
Its director Mahmood Amiry-Moghaddam wrote that authorities "cut electricity and machine gun shooting is heard … Unconfirmed reports of protesters being killed or wounded."
He posted an audio file in which screams are clearly heard amid continuous gunfire.
Kurds make up one of Iran's most important non-Persian ethnic minority groups and generally adhere to Sunni Islam rather than the Shiism dominant in the country.
Hengaw had on Saturday warned the situation was "critical" in the town of Divandarreh in the western province of Kurdistan, where government forces had shot dead at least three civilians.
It also expressed concern on Sunday about the situation in other Kurdish-populated towns with explosions heard in Bukan and Saqez, as well as gunfire in Bukan.
Reinforcements of the security forces were sent to the city of Mahabad in western Iran, rights groups said, while images and audio files of heavy gunfire and screams were posted...