Iranian security forces, including the pro-government Basij militia, are trying to quell growing nationwide protests that erupted after a woman died in the custody of the morality police last week.
Four members of the Basij were killed in the unrest, including one who was stabbed, Iranian media said.
Here are some facts about the Basij, shock troops that have been at the forefront of repressing popular unrest, making them a direct target for protesters angered by the lack of political and social freedoms in Iran.
The Basij, formally known as the Organization for the Mobilization of the Oppressed, was created as a paramilitary volunteer militia by the founder of the Islamic Revolution, Ayatollah Ruhollah Khomeini, in 1979.
The Basijis, most of whom stem from poor, rural backgrounds, are famed for their "human waves" attacks against Saddam Hussein's troops in the 1980-88 war with Iraq, which were intended to overwhelm the defenders by the sheer weight of numbers and regardless of high casualties.
In peacetime, they enforce Iran’s Islamic social codes, acting as a morality police at checkpoints and parks, at other times crushing protests. The force is also deployed during natural disasters and has a presence in government institutions.
Analysts say Basij volunteers may number in the millions, with 1 million active members.
In 1981, the Basij was incorporated into the organizational structure of the Revolutionary Guards, the main paramilitary force in charge of protecting the Shiite clerical ruling system and revolutionary values. After Iran's war with Iraq ended in 1988, the Basij were not disbanded and continued as a religious militia that provides the country’s establishment with manpower and a heavy presence during pro-government rallies.
The morality police are often made up of and backed by the Basij, which often acts as the state's iron fist when protests erupt.
Basij have a presence in every Iranian university to monitor people's dress and behavior as higher learning is where Iranian male and females meet for the first time in a mixed educational environment.
A Basiji usually belongs to parts of Iran's religiously traditional and pro-regime youth. They are tightly affiliated to the country's hardline faction and represent one hand of Iran’s own culture war, pitting its more conservative elements against more liberal citizens.
Role in latest demonstration
Semi-official media outlets have reported the death of at least five security personnel in different Iranian cities over the past week, including four members of the Basij.
Pro-government media said the slain security forces had been targeted by "rioters and gangs" while trying to bring back order and stop protesters from destroying public property. One Basij died from stab wounds while another was killed by gunshot, according to media.
Fars news, an agency close to the Revolutionary Guards, shared a video on Telegram of the work of the Basij during the current unrest. The footage showed the volunteers putting out small fires burning in waste containers as they cleared up streets after the protests.
Basij interviewed in the video said "rioters" had closed roads in the capital city, endangered ordinary people, destroyed public property, and removed conservative veiling from religious women.
They added they were mobilized late at night to protect the "honor and property of the people" and that they would not allow "a few sissies" to disrupt the order of the country. "We will stand till the end (to protect the regime)," one was heard saying in the footage. Reuters could not verify the video.