DUBAI, United Arab Emirates (AP) — Iranian protesters clashed with police in a town near the capital on Thursday, reportedly killing or wounding a number of members of the security forces, who at one point dropped stun grenades on the demonstrators from helicopters.

It was the latest in a wave of demonstrations that have convulsed Iran for more than six weeks and mark one of the biggest challenges to the country’s clerical rulers since they seized power in the 1979 Islamic Revolution.

The protesters had gathered in Karaj, just outside Tehran, to mark the 40th day since the shooting death of Hadis Najafi, 22, one of several young women to have been killed during the protests. The demonstrations were ignited by the death of another woman held by the country’s morality police.

The 40th day after someone’s death has great symbolism in Shiite Islam and is marked by public mourning. Commemorating protester deaths has given momentum to the ongoing demonstrations, just as it did during the 1979 revolution that overthrew a Western-backed monarchy.

Videos circulated online showed thousands of protesters in Karaj and clashes with police. In one of them, a helicopter flies over the protesters and drops flash grenades in an attempt to disperse them before landing in the middle of a highway. Government supporters on social media said the helicopter was sent to aid wounded policemen.

The state-run IRNA news agency tweeted that police were attacked in the area and posted a video showing a police pickup truck that had crashed into a concrete barrier on a highway.

It was not immediately clear what caused the crash, but videos showed protesters hurling rocks at the vehicle and a man firing into it as at least three wounded individuals were inside. IRNA later posted photos of what appeared to be two lifeless bodies.

The semiofficial Tasnim news agency reported that three policemen were seriously wounded in clashes with protesters. It was not immediately clear it it was referring to the same event. Tasnim also reported that protesters set fire to a police kiosk and van.

The semiofficial Fars news agency said a member of the paramilitary Basij militia was stabbed to death in Karaj.

Iranian authorities heavily restrict media coverage of the protests and have periodically shut down internet access across the country, making it difficult to confirm details of the unrest.

The demonstrations were ignited by the Sept. 16 death of 22-year-old Mahsa Amini, who had been detained by the morality police for allegedly violating Iran’s strict dress code for women. Authorities say she died because of a health condition and was not mistreated, but her family has cast doubt on that account and the protesters accuse the police of beating her to death.

The first big protests erupted at Amini’s funeral in her hometown in the Kurdish region of Iran. The near-daily demonstrations continued, flaring up again 40 days after she was buried.

The protests were initially focused on Iran’s enforcement of the Islamic headscarf, or hijab, with crowds of young women removing theirs during raucous street protests. The demonstrations rapidly grew into calls for the overthrow of the theocracy that has ruled Iran for more than four decades.

Security forces have sought to quash dissent, killing at least 270 people and arresting some 14,000, according to rights groups.

Iran’s judiciary has said more than a thousand people who had a central role in the protests would be brought to trial in Tehran over their “subversive actions,” including assaulting security guards and torching public property. Authorities have announced charges against hundreds of people in other Iranian provinces, some accused of “corruption on earth” and “war against God,” offenses that carry the death penalty.