Human Rights Watch called Tuesday on Libyan authorities to immediately investigate the alleged ill-treatment of detainees including a son of slain dictator Muammar Gaddafi at a prison in Tripoli.
An undated video published by Arabic news website Clearnews on August 2 appears to show officials and guards at al-Hadba prison ill-treating several detainees, including Gaddafi's third-oldest son Saadi, the rights watchdog said.
"The graphic video that seems to show prisoners being beaten raises serious concerns about the methods used to interrogate Saadi Gaddafi and other detainees at al-Hadba prison," said Joe Stork, HRW's deputy Middle East director.
"The Tripoli authorities need to urgently establish exactly what did occur, put in place measures to protect all detainees from abuse, and hold anyone responsible for that kind of treatment to account."
Libya has been rocked by conflict since Gaddafi's overthrow, with rival governments and militias battling for control of the oil-rich country's main cities.
Al-Hadba is controlled by the Libya Dawn militia coalition, which supports the self-declared authority in Tripoli to the west, rival to the internationally recognized Libyan government in al-Bayda and Tobruk to the east.
Saadi was extradited to Libya in March 2014 from Niger, where he had sought refuge after the 2011 uprising.
In April 2014, Libya's official television station aired videos showing Saadi in a blue prison uniform apparently confessing to having worked against the country's political system, from what appeared to be his jail in Tripoli, HRW said.
A court in al-Hadba on July 28 sentenced Seif al-Islam, Gaddafi's second son and once heir apparent, and eight of his aides to death for crimes during the 2011 revolt, in a verdict condemned by rights campaigners.
Three of Gaddafi's seven sons died in the uprising. Gaddafi himself was captured and killed by rebels in October 2011.