Suspected Boko Haram militants in Cameroon are dying in jail of disease, malnutrition and in some cases torture, Amnesty International says.
More than 1,000 suspects are being held in horrific conditions, with at least eight dying each month, the rights group's said in a report.
Cameroon's government has dismissed the report as false and misleading.
The Islamist group Boko Haram frequently carries out attacks in Cameroon, often using suicide bombers.
Almost 500 have died in the violence this year in Cameroon, which borders Nigeria where the insurgents are based.
Many of the people accused of supporting Boko Haram by the authorities in Cameroon have been arrested without any reasonable suspicion they had committed a crime, Amnesty's report said.
Extrajudicial killings by the security forces were also documented in the report, including six cases where it says suspects were tortured to death.
Amnesty did acknowledges that Cameroonian officials were working to relieve overcrowding and improve water supplies.
Boko Haram at a glance:
Founded in 2002 in Nigeria, initially focused on opposing Western-style education. Boko Haram means "Western education is forbidden" in the Hausa language
Launched military operations in 2009
Thousands killed, mostly in north-eastern Nigeria, hundreds abducted, including at least 200 schoolgirls
Joined so-called Islamic State, now calls itself IS's "West African province"
Seized large area in north-east, where it declared caliphate, and attacked neighbouring countries
Regional force retook most territory last year, but suicide attacks continue.