Tehran: The man stood outside the notorious Evin Prison in Tehran on Sunday, his hands deep inside his pockets as snow continued to fall. His son Majid had been inside the prison for over a week, after being arrested during the largest anti-government demonstrations Iran has seen in years.

“My wife and I are here every day,” said the man, who gave only his first name, Hussain. “I don’t want trouble. I just want my son released.”

Majid, a 32-year-old employee at a telecommunications company, calls from prison daily. He had not been protesting at all, his father insists, and was arrested by mistake.

Members of Iran’s ruling establishment have taken turns assigning blame for the protests in more than 80 cities that have resulted in at least 21 deaths and shined a light on the country’s declining economic conditions, corruption and a lack of personal freedom. Some have accused foreign “enemies,” including the United States, Israel and Saudi Arabia, of organising and financing the movement.

More than 500 people have been arrested in Tehran alone since the demonstrations began on Dec. 28. Local news organisations say that more than 1,000 have been detained nationwide, and even that is probably a conservative estimate. The average age of those arrested is younger than 25, the deputy interior minister, Hussain Zolfaghari, told the semiofficial website Jamaran.

Based on reports from family members and friends outside Evin Prison on Sunday, as well as official sources, dozens of people have been released, but hundreds more remain in prison.

A group of reformist activists wrote an open letter published Sunday on the front page of the newspaper Etemaad calling for the release of those arrested during the demonstrations, saying that Iranians had the right to protest peacefully.

“People feel belittled and hopeless,” the letter said.

There were more than 100 people gathered outside Evin Prison on Sunday: family members and friends of the detained, the women shielding themselves from the snow with umbrellas; a well-known political activist, Mohammad Nourizad; and a group of dervishes that had set up a makeshift camp under one of the prison’s watchtowers, singing an old song from their native province, Lorestan.

“Oh mother, mother, it is time for fighting, it is time to make friends with the rifle,” a man with an imposing mustache sang, with others repeating the lines after him.

They gathered around a campfire, having brought an ample supply of wood and tents in which to sleep. They had, effectively, set up a protest camp in front of the prison.

“The political prisoners must be freed,” they chanted as people filmed them with their phones, and as guards carrying machine guns on their shoulders looked down from walls and watchtowers above.

Evin Prison, a sprawling complex built partly inside a mountain, is Tehran’s oldest and most notorious prison. It has played an important role in Iran’s contemporary history, housing political and criminal prisoners since 1972. Some of the cells were designed for solitary confinement, and the Islamic Revolutionary Guards Corps and the Ministry of Intelligence and Security control their own sections of the building.

Iran is a country where activism or political dissent can often lead to charges and imprisonment. Hundreds of journalists, bloggers and activists have been detained over the years. Charges can come down even against those seemingly not involved in opposition politics, like Jason Rezaian, an Iranian-American reporter for The Washington Post who was held in Evin Prison for 544 days on charges of espionage, a claim he strongly denies.

When Iran faced its last major anti-government demonstrations, the Green Movement of 2009, millions took to the streets and thousands were arrested, requiring temporary holding centres to be opened because Evin was overcrowded. In one, the Kahrizak detention centre in Tehran, some protesters were tortured, and three died.

Iran’s supreme leader called for an investigation of that case, and several officers were given jail sentences. Not all have served those sentences, however, the local news media has reported.

Ali, a plump man wearing a brown beret who would not give his surname for fear of retribution by authorities, was waiting in the snow outside Evin Prison for the release of his friend Hussain, who was arrested on Dec. 29.

Hussain had been at the demonstrations because “he was angry, like many people,” Ali said. Hussain soon realised a man had grabbed the cellphone of a woman who had been filming the protesters.

“Hussain chased him, but he turned out to be a plainclothes police officer,” Ali said. “I’m bringing the deed of his house so he can post for bail.”

The entrance of Evin Prison is near a busy highway, and metal sheets have been placed on overpasses to prevent people from looking down. But a side road provides direct access to the prison, and a parade of Iranian-made cars, a garbage truck, motorcycles and a high-end-model Mercedes-Benz drove past at one point Sunday, with many rolling down their windows to see the people waiting in front of the prison.

“Poor families,” said Hamid Mousavi, a retiree driving a taxi. “They must be so worried.”

Siavash, who works for the Telecommunications Ministry, said he had come to Evin to bail out his brother-in-law, Siamak, whom he described as a womaniser.

“He wanted to meet women, I guess, and have some fun,” Siavash said. “He’ll be freed today, I’m happy. He’s been calling us a couple of times a day. He wants to come home.”