Human rights group Hengaw has posted a video showing Iranian government forces shooting at civilian homes and another in which gunfire and cries could be heard during crackdowns on protests in western Iran.
Amnesty International said there were reports that Iranian government forces had used firearms indiscriminately in Sanandaj.
It reported that dozens of civilians had been killed and 400 injured across the region since Sunday.
But it warned that the death toll might be higher because authorities were disrupting local internet and mobile networks.
Protests against the clerical establishment have swept across Iran since the death of Mahsa Amini three weeks ago, a Kurdish woman from the western city of Saqqez who fell into a coma after being detained by morality police in Tehran for allegedly violating the strict hijab law.
The unrest is now considered the most serious challenge to the Islamic Republic since its inception in 1979.
Iran’s leaders have accused foreign enemies and exiled opposition groups of fomenting “riots” that they will not tolerate.
Hengaw reported on Tuesday that over the past three days protests had taken place in 10 areas of Kurdistan, Kermanshah and West Azerbaijan provinces, with Sanandaj the epicentre of the unrest and the crackdown by authorities.
The Norway-based group posted videos which it said showed intense clashes between protesters and the Iranian government forces in the city on Monday night. Repeated gunfire can be heard in the footage, as well as cries and shouts.
According to Hengaw, other footage showed a crowd coming under attack, empty bullet cases, shotgun cartridges and tear-gas canisters left on the streets, and security personnel shooting directly towards homes.
Thousands of people have also reportedly been arrested in the crackdown.
On Monday, dozens of employees blocked roads outside the Assaluyeh petrochemical complex in Bushehr province and shouted: “Do not fear, we stand together.” A regional official insisted it was related to a wages dispute.