Iran issued a second death sentence in three days and clashes killed at least six people as women-led protests over Mahsa Amini's death in custody entered a third month Wednesday.

Street violence raged across Iran overnight as protests sparked by the September 16 death of Amini intensified on the anniversary of a lethal 2019 crackdown.

Amini, a 22-year-old Iranian woman of Kurdish origin, died in the custody of the notorious morality police after her arrest for an alleged breach of Iran's strict dress code for women.

"We'll fight! We'll die! We'll take back Iran!" dozens of protesters could be heard chanting around a bonfire on a Tehran street overnight, in a video published by the 1500tasvir social media monitor.

In widely shared video verified by AFP, security forces appear to open fire on dozens of commuters at a Tehran metro station, causing them to scramble and fall over each other on the platform.

Organisers of the protests have called for three days of actions to commemorate hundreds killed in the "Bloody Aban" -- or Bloody November -- demonstrations that erupted on November 15, 2019 after a shock decision to hike fuel prices.

Bazaar shops were shuttered and students boycotted class before people hit the streets after dark, chanting anti-government slogans and braving tear gas, according to videos posted online.

But the 1500tasvir monitor said families of those killed in the 2019 crackdown "were forced to cancel the ceremonies" as a result of "the Islamic republic's threats and pressure".

'Guards killed'

The Iranian authorities have struggled to contain the protests, which have seen women remove and burn their headscarves and face off with the security forces on the street.

State media said "rioters" -- a term used by officials to describe protesters -- killed two members of the Revolutionary Guards and a member of its Basij paramilitary force on Tuesday.

Guards Colonel Reza Almasi was shot dead in Bukan, a city in Amini's home province of Kurdistan, and another Guards member, Reza Azabar, was gunned down in Kamyaran, a Kurish majority city in West Azerbaijan province, the official IRNA news agency reported.

The Basij member died after being hit by a Molotov cocktail in the southern city of Shiraz, it added.

Three protesters have been killed, two in Sanandaj and one in Kamyaran by direct fire from government forces, Oslo-based rights group Hengaw said.

The unrest was fanned by fury over the dress rules for women, but has grown into a broad movement against the theocracy that has ruled Iran since the 1979 Islamic Revolution.

It has shown no sign of abating despite the authorities' use of lethal force and a campaign of mass arrests that has snared activists, journalists and lawyers.

Oslo-based group Iran Human Rights said on Saturday that security forces had killed at least 326 people, including 43 children and 25 women, in the crackdown on the Amini protests.

IHR said at least 15,000 people have been arrested -- a figure the Iranian authorities deny.

Fear of mass executions

The judiciary said a revolutionary court on Tuesday handed down the second death sentence over the "riots" that have rocked the country since Amini's death.

The unnamed defendant was accused of "terrorising people in the street using a bladed weapon, setting fire to the motorcycle of a citizen, and attacking a person with a knife", its Mizan Online website reported.

It came three days after a court issued the first death sentence in connection with the protest movement that has shaken the Islamic republic's clerical leadership.

Five others have been sentenced to prison terms of between five and 10 years for "gathering and conspiring to commit crimes against national security and disturbing public order", Mizan said.

IHR director Mahmood Amiry-Moghaddam said the second death sentence was expected and that more are likely to be announced "one by one to minimise the reactions".

"We strongly condemn the death sentences issued by the Islamic republic judiciary, which is part of the oppressive regime and not an independent judicial system," he told AFP.

"Protesters don't have access to lawyers in the interrogation phase, they are subjected to physical and mental torture to give false confessions and sentenced based on the confessions by the revolutionary courts.

"The international community must send a strong warning to the Islamic republic that execution of protesters will have severe consequences," said Amiry-Moghaddam.

"We fear mass executions, unless the political cost of executions increases significantly," he told AFP.