Leaked surveillance footage from Iran's notorious Evin prison that shows guards beating inmates and committing other abuses is real, the head of the country's prison service has said.
On Tuesday, Mohammad Mehdi Hajmohammadi apologised for the “unacceptable behaviour” and “mistakes” revealed in the video.
Footage showing conditions in the prison was leaked online by a little-known group of hackers called Adalat Ali.
It shows prison officials standing in a control room as monitors display a message from the hackers: “Cyberattack. General protest until the freedom of political prisoners."
“We want the world to hear our voice for freedom of all political prisoners," Adalat e-Ali told the AP.
The video includes footage of a frail and struggling inmate being dragged through an area of the prison and up a flight of stairs.
“Regarding the pictures from Evin prison, I accept responsibility for such unacceptable behaviour and pledge to try to prevent any repeat of these bitter events and to deal seriously with the wrongdoers,” Mr Hajmohammadi said.
It was a rare admission of human rights abuses in Iran, where authorities have often dismissed criticism of the regime's actions.
Footage shared by Radio Farda, the Iranian branch of the US government-funded Radio Free Europe/Radio Liberty broadcast service, shows inmates and guards fighting.
Other clips show a man smashing a bathroom mirror to try to cut his arm and prisoners' sleeping conditions are also revealed, with bunk beds stacked three high against the walls of small cells.
Rights groups have condemned abuses they said are committed at the prison, which was built in 1971. Political prisoners and those facing security charges are among those detained there.
“The [Evin] authorities use threats of torture, threats of indefinite imprisonment and torture of family members, deception and humiliation, multiple daily interrogations lasting up to five or six hours, denial of medical care and denial of family visits,” Human Rights Watch has previously said.
People who protested against the contested re-election of hardline president Mahmoud Ahmadinejad in 2009 were locked up in the prison and reports of abuse at the time led MPs to push for reforms and CCTV cameras were installed.
In 2017, Iran invited foreign officials to tour the prison to counter negative press.
Rights group Amnesty International called the move a “crude PR stunt” and said measures were taken to ensure the visitors did not see the prison's inhumane conditions.
Research by Amnesty International and other human rights groups has suggested inmates are subjected to inhumane and unsanitary conditions.
“Chronic overcrowding, severely limited hot water, poor ventilation and infestations of cockroaches and mice, particularly near kitchen areas, are among the most common complaints,” Amnesty International's Iran researcher and human rights lawyer Raha Bahreini said at the time.
“Prisoners have described being forced to sleep on the floor, including during cold winter months, due to a shortage of beds and being fed barely edible meals.
"Prisoners who are lucky enough to afford to do so can purchase food at their own expense from the prison shop.”
Dual citizens such as Iranian-Canadian journalist Maziar Bahari, German-Iranian architect Nazanin Taghavi and British-Iranian charity worker Nazanin Zaghari-Ratcliffe are among those who have been detained at the prison.
Some wards are managed by Iran's Islamic Revolutionary Guard Corps, the US State Department said.