Campaign group Human Rights Watch (HRW) says Cameroon's authorities held more than 100 detainees incommunicado and tortured many of them, following a riot in one of the country's biggest prisons.
Last month inmates set fire to parts of Kondengui maximum security prison in the capital, Yaoundé, and some even live-streamed on Facebook the initial protest from their mobile phones.
Many people accused of being separatist rebels from the Anglophone regions are held in that facility, and in video footage from the 22 July protest prisoners were heard chanting pro-independence slogans as well as decrying their treatment and conditions.
HRW reports that among the group sent to State Defense Secretariat the next day, where the alleged torture began, were suspected separatists as well as suppporters of the opposition CRM party.
Cameroon's government has not commented on the allegations of torture, but confirmed the transfer of dozens of inmates from Kondengui to unspecified facilities.