This week's protests coincide with the third anniversary of "Bloody Aban" -- or Bloody November -- when hundreds were killed in a crackdown on street violence that erupted over a shock overnight decision to hike fuel prices.
Security forces on Thursday killed one protester in Bukan and two in Sanandaj, a flashpoint where mourners were paying tribute to "four victims of the popular resistance" 40 days after they were slain, the Oslo-based Hengaw rights group said.
It said a member of the security forces was also killed later in Sanandaj, where people thronged the streets even as the sound of gunfire was heard in a video published by Hengaw and verified by AFP.
"Death to the dictator," protesters chanted in another online video as they marched down a street in Sanandaj filled with bonfires and cars whose horns blared, directing their fury at Iran's supreme leader Ayatollah Ali Khamenei.
The tradition in Iran of holding a "chehelom" mourning ceremony 40 days after a death has fuelled the demonstrations that have become the regime's biggest challenge from the street in decades.
Fears are growing that the regime is turning "more violent after being unable to suppress the people for two months", said Saeid Golkar, from the University of Tennessee at Chattanooga.
Speculation has mounted that Iran's leadership has decided to crush the protest movement in the same way that it did in November 2019, when security forces killed at least 304 people, according to Amnesty International.
The demonstrations were sparked by the death of 22-year-old Amini on September 16, after her arrest for allegedly violating Iran's strict dress code for women.
The unrest has been fanned by fury over the brutal enforcement of the mandatory hijab law, but has grown into a broad movement against the theocracy that has ruled Iran since the 1979 Islamic Revolution.
Gunmen on motorcycles killed nine people in two mysterious attacks Wednesday, state media said, as the protests intensified.
In the southwestern city of Izeh, "a terrorist group took advantage of a gathering of protesters" to shoot dead seven people -- including a 45-year-old woman, two children aged nine and 13, and a police officer, the official IRNA news agency said.
It was the second attack the authorities have blamed on "terrorists" in the two months since the protests broke out, after at least 13 people were killed at a shrine in the southern city of Shiraz on October 26.
But a family member of the nine-year-old boy killed on Wednesday, identified as Kian Pirfalak, accused security forces of carrying out the attack, in a tweet shared by Radio Farda, a US-funded Persian station based in Prague.
"He was going home with his father and was targeted with bullets by the corrupt regime of the Islamic republic. Their car was attacked from all four sides," the unidentified family member is heard saying in an audio recording.
In a separate attack hours later in Iran's third city Isfahan, two assailants on a motorcycle shot dead two members of the Basij paramilitary force and wounded another two, Fars news agency said.
Elsewhere, Hengaw accused the security forces of killing at least 10 people within a 24-hour period up until late Wednesday at protests in the cities of Bukan, Kamyaran, Sanandaj and Amini's hometown of Saqez.
Iran's Foreign Minister Hossein Amir-Abollahian accused Israel and its allies of plotting against the Islamic republic.
Security services, Israel and Western politicians had "made plans for a civil war and the destruction and disintegration of Iran", Amir-Abollahian tweeted.
But, he added, they "must know that Iran is not Libya or Sudan" and that the "wisdom of our people has thwarted their plan".
General Hossein Salami, head of the Revolutionary Guards, said Iran was facing a "conspiracy".
"The United States, England, Germany, France, Israel, Saudi Arabia and their allies are preparing to fight God, his prophet and the martyrs," Salami said, quoted by Fars news agency.
Iran Human Rights, another Oslo-based organisation, said Wednesday that security forces had killed at least 342 people, including 43 children and 26 women, since the start of protests.
Amnesty International said Iran was seeking the death penalty for at least 21 people in "sham trials designed to intimidate" protesters.
"The crisis of impunity prevailing in Iran is enabling the Iranian authorities to not only continue carrying out mass killings but also to escalate the use of the death penalty as a tool of political repression," Amnesty's Diana Eltahawy said.