At least four prisoners have been killed and 61 others injured after a fire broke out at Tehran’s Evin prison overnight following a fight between inmates, the official state news agency IRNA reported quoting the country’s judiciary.

Smoke inhalation was said to be the cause of the deaths, IRNA reported on Sunday, adding 10 inmates are hospitalised with four in “critical condition”.

The facility mostly holds political prisoners, including Iranians with dual nationality. Families of about two dozen political prisoners have called to say they are unharmed, according to their accounts on social media.

The prison has long been criticised by Western rights groups and was blacklisted by the United States government in 2018 for “serious human rights abuses”.

The incident took place as nationwide protests over the death in detention of Mahsa Amini, a 22-year-old Iranian woman, entered a fifth week.

The protests have posed one of the most serious challenges to the Iranian government since the 1979 revolution, with demonstrations spreading across the country and some people chanting slogans against Supreme Leader Ayatollah Ali Khamenei.

State TV on Sunday aired footage of the fire’s aftermath, showing scorched walls and ceilings in a room it said was the upper floor of a sewing workshop at the prison. Tehran prosecutor Ali Salehi said the prison unrest was not related to the nationwide protests and the situation was peaceful after the incident.

The fire started at about 10pm (6.30pm GMT), Al Jazeera’s Resul Sardar said, adding that it involved different units of the prison.

Damage caused by a fire inside the building of the Evin prison

“Officials here say there were clashes between prisoners and that some of those prisoners have set the fire in the warehouse, in the sewing workshop of the prison,” Sardar said, referring to a statement made earlier by Tehran Governor Mohsen Mansouri.

“However some witnesses are saying that some Molotov cocktails were thrown into the prison and that they started the fire. Right after that, we have seen security forces firing and also using tear gas to disperse people,” he added.

A witness contacted by the Reuters news agency said roads leading to Evin prison have been closed to traffic. “There are lots of ambulances here,” he said. Another witness said families of inmates gathered in front of the main prison entrance. “I can see fire and smoke. Lots of special forces,” the witness said.

A security official said calm had been restored at the prison, while IRNA reported that “the situation is currently completely under control”. But the first witness told Reuters that ambulance sirens could be heard and smoke still rose over the prison.

Early on Sunday, IRNA carried a video it said showed parts of the prison damaged by fire. Firefighters were seen dousing the debris with water, apparently to prevent the blaze from reigniting.

‘Numb with worry’

The detainees include French-Iranian academic Fariba Adelkhah and US citizen Siamak Namazi, whose family said he was taken back into custody this week after a temporary release.

Reacting to reports of the fire, Namazi’s family said in a statement to the AFP news agency shared by their lawyer that they were “deeply concerned” and had not heard from him.

They urged Iran’s authorities to grant him “immediate” means to contact his family and to give him a furlough “as he clearly isn’t safe in Evin Prison”.

The sister of another US citizen held at Evin, businessman Emad Shargi, said in a Twitter post his family was “numb with worry”.

An unnamed Iranian official told the Tasnim news agency that none of the political prisoners was involved in Saturday’s unrest.

“No security prisoner was involved in today’s clash between prisoners, and basically the ward for security prisoners is separate and far from the wards for thieves and those convicted of financial crimes,” the official was quoted as saying.

Asked about the prison fire, US President Joe Biden told reporters during a campaign trip to Portland, Oregon: “The Iranian government is so oppressive.”

He said he was surprised by “the courage of people and women taking [to] the street” in the recent protests and had enormous respect for them. “It’s been really amazing,” he added. “They’re not a good group, in the government.”

US Department of State spokesman Ned Price tweeted, “We are following reports from Evin Prison with urgency. We are in contact with the Swiss as our protecting power. Iran is fully responsible for the safety of our wrongfully detained citizens, who should be released immediately.”

Human Rights Watch has accused the prison authorities of using threats of torture and indefinite imprisonment, as well as lengthy interrogations and denial of medical care for detainees.

Protests erupted after the September 16 death of Amini, who was arrested by Iran’s morality police for wearing an improper hijab. She died in custody. A coroner’s report said she did not suffer blows to the head or vital organs.

Amini’s family have refuted the official accounts that attributed the 22-year-old’s death to conditions arising after a brain tumour surgery at age eight.

Although the unrest does not appear close to toppling the government, the protests have widened into strikes that have closed shops and businesses, touched the vital energy sector and inspired brazen acts of dissent against Iran’s religious rule.

On Saturday, protesters across Iran chanted in the streets and in universities against the country’s religious leaders.

A video posted by the Norway-based organisation Iran Human Rights purported to show protests in the northeastern city of Mashhad, Iran’s second-most populous city, with demonstrators chanting “Clerics, get lost”, and drivers honking their horns.

Videos posted by the group showed a strike by shopkeepers in the northwestern Kurdish city of Saqez – Amini’s hometown. Another video on social media showed female high school students chanting “Woman, Life, Freedom” on the streets of Sanandaj, the capital of Kurdistan province.

The authenticity of the videos could not be verified immediately.

The Iranian activist news agency HRANA said online that 240 protesters had been killed in the unrest, including 32 minors. It said 26 members of the security forces were killed, and nearly 8,000 people had been arrested in protests in 111 cities and towns and some 73 universities.

But the official death toll is much lower than estimated by rights groups and protesters.

Among the casualties have been teenage girls whose deaths have become a rallying cry for more demonstrations demanding the downfall of Iran’s government.

Protesters called on Saturday for demonstrations in the northwestern city of Ardabil over the death of Asra Panahi, a teenager from the Azeri ethnic minority who, activists alleged, was beaten to death by security forces.

Officials denied the report and news agencies close to the Islamic Revolutionary Guard Corps quoted her uncle as saying the high school student had died of a heart problem.