Iranian activists arrested in a crackdown on protests sparked by the death of Mahsa Amini are at risk of torture or even dying behind bars, human rights groups have warned.

Amini, 22, died in September three days after she was arrested by vice squads in Tehran for allegedly violating the Islamic Republic’s strict dress code, sparking protests that have been going on for more than a month.

Shocking images emerged Thursday of the arrest of freedom of expression activist Hossein Ronaghi, who was put in a chokehold and dragged away while presenting himself to prosecutors.

He has been held in Tehran’s Evin prison since his arrest on September 24, and his family say he is at risk of dying of kidney disease.

They also say that his legs are broken.

Ronaghi is just one of several prominent rights activists, journalists and lawyers who have been arrested and who supporters fear may never get out alive from the notorious facility where most political prisoners are held.

Eight people died in a fire in Evin on October 15, according to the authorities.

Concerns for the well-being of prisoners only increased as activists accused the authorities of firing tear gas and metal pellets at the prison, although none of the political prisoners were reported to have been harmed.

“Detainees, often forcibly disappeared, are at serious risk of torture and death. Urgent action by the international community is crucial at this point,” said Mahmood Amiry-Moghaddam, director of the Oslo-based group Iran Human Rights.

According to IHR, thousands across the country were arrested in the raid, including at least 36 journalists, 170 students, 14 lawyers and more than 580 civil society activists, including workers and union officials.

Roya Boroumand, director of the Washington-based Abdorrahman Boroumand Center, said the situation is being exacerbated by the sheer number of new prisoners being transferred to prisons, including Evin and Fashafouyeh Greater Tehran Prison.

“We are very concerned about the treatment of detainees,” she told AFP.

Overcrowding means it has “no choice but to alternate between sitting and sleeping” in areas including prison gyms.

Analysts say the mass arrests are a key strategy under Ayatollah Ali Khamenei to quell the nationwide wave of protests that pose one of the biggest challenges to Iran’s Islamic system since the 1979 revolution.

Ronaghi, a Wall Street Journal contributor, has for years been one of the most fearless critics of the Islamic Republic still alive in the country.

Security forces made an initial attempt to arrest him on September 22 when he was giving a live interview to Iran International TV, but he managed to slip out of his home, he said at the time.

He came out of hiding two days later but was immediately arrested along with his lawyers.

After the fire that ripped through the prison, Ronaghi “had a brief phone call with my mother but could only say a few words and could barely speak due to poor health,” his brother Hassan Ronaghi wrote on Twitter.

“Hossein’s life is in danger,” Hassan wrote in his last tweet on Wednesday.

After the Evin fire, Amnesty International called for access to independent monitors “to protect detainees from further unlawful killing, torture and other ill-treatment”.

Activist Majid Tavakoli, who has been jailed repeatedly in Iran in recent years, including after disputed 2009 elections, remains in prison following his September 23 arrest.

His family say they have not heard from him since the fire. “Why can’t a man be free whose only tool is his brain? Is thinking a crime?” His wife tweeted.

Arash Sadeghi was only released from prison last May after several years in prison. He was jailed in Evin on October 12 despite suffering from chondrosarcoma, a rare type of bone cancer.

His father tweeted a picture of a dozen boxes of medicines he needs.

“One can imprison his body, but his soul is always with the people and the prisoners he does not know,” he wrote.

The IHR expressed concern that several activists remained incommunicado behind bars, including journalist and activist Golrokh Iraee and prominent tech blogger Amir Emad Mirmirani, known as Jadi.

The human rights group said some detainees “made self-incriminating confessions on television under duress and torture” and were also subjected to verbal abuse during detention.

Detainees “testified during interrogation that they were severely beaten, tortured and deprived of food and clean drinking water,” Boroumand said.

“Detainees are left with buckshot and broken limbs (and) without medical attention.”