Prominent members of the outlawed Islamic Renaissance Party of Tajikistan opposition party (IRPT) were among those killed in a prison riot on Monday, the Tajik government confirmed.
The insurrection, which took place in Vakhdat, about 10km east of the capital, Dushanbe, claimed the lives of at least 32 people, including three prison guards and 29 inmates, the government said.
Authorities said they believed the Islamic State of Iraq and Levant (ISIL or ISIS) group was responsible for setting off the disturbance after a fight broke out between members of the group and IRPT.
According to the justice ministry, members of ISIL armed with knives killed three security guards before executing several fellow prisoners.
"In order to intimidate the other prisoners, the Islamic State members executed five people and 10 others were savagely beaten," a statement from the ministry said, referring to the ISIL group.
At the time of publication, ISIL had yet to claim responsibility.
Maran Turner, the executive director of the prisoners of conscious Freedom Now organisation, called on the Tajik government to ensure the protection of all prisoners in its custody and to "conduct a thorough, transparent, and independent investigation into the riot".
"We express our deepest condolences to the families of Sattor Karimov, Saeed Qiyomiddin Ghozi, and Jomahmad Boev," Turner said.
"The deaths of these men, who were imprisoned on politically motivated charges, is a travesty of justice," Turner added.
Karimov was a member of IRPT's supreme political council, and was sentenced to 26 years in prison in 2016 for alleged involvement in a coup attempt.
His peer, Ghozi, was a founding IRPT member who was abducted in St. Petersburg, Russia, in 2017 and was forcibly taken to Tajikistan by government agents.
He was sentenced to 25 years in prison before the penalty was reduced to eight years.
Relatives of the detained activists informed human rights groups that the detainees were subjected to torture and kept incommunicado.
Last November, ISIL claimed responsibility for another Tajik prison riot, which followed a deadly attack by its followers on tourists in July 2018.
A Tajik man, who joined ISIL before handing himself over to the US-backed Syrian Democratic Forces (SDF) in Syria, told Reuters news agency last month that many foreigners who enlisted in its self-declared caliphate of ISIL were jailed or killed for trying to leave.
Tajikistan has offered amnesty to those who quit the armed group and return home, provided they have committed no other crimes.