According to activists, one prisoner was killed and 17 others injured in an outbreak of violence in a prison in northern Iran over a planned execution.
The confrontations at the Karaj detention center broke out on Saturday when prisoners protested against the transfer of an inmate to solitary confinement before his execution, the Iran Human Rights organization (IHR) said on Sunday.
The victim died from a shot in the head.
However, the Iranian authorities said that one detainee died after a conflict between inmates.
The Chief Justice of Albors Province said the riots began in the section where prisoners are serving sentences for drug-related offences.
Prisoners had set bed covers on fire.
Since then, however, calm has returned.
"Death to the Dictator"
It is the third major incident in an Iranian prison since the wave of protests began in the country.
The demonstrations were triggered by the death of the young Kurdish woman Mahsa Amini in September in custody of the vice squad.
Karaj is an important center of the protests.
According to the Norway-based activist organization IHR, the prisoners in Karaj chanted anti-government slogans, including "death to the dictator" in reference to Ayatollah Ali Khamenei, the country's spiritual leader.
According to the information, inmates also blocked the entrances to the prison and destroyed surveillance cameras.
So far this month, Iran has carried out two death sentences in connection with the wave of protests in the country.
The human rights organization Amnesty International said on Friday that at least 26 other people were at risk of being executed in connection with the protests.
In October, a fire broke out in a prison in the capital Tehran, killing at least eight people.
In the same month, inmates mutined in a detention center in Rascht, capital of north-western Gilan province.
