China's worst prisons are those in minority areas, such as Xinjiang, Tibet or Inner Mongolia, and the worst-treated prisoners are minorities, as well as Falun Gong believers, rights groups say.
Uighur "separatists" -- those accused of fighting for an independent Muslim state in northwest China's Xinjiang region -- are severely abused.
"They are treated worse because they are seen as enemies of the state, separatists or backward," says Nicolas Becquelin, research director for Human Rights in China.
Uighurs have told of guards pouring hot pepper oil on their open wounds after being beaten, says Dilxat Raxit, spokesman for the World Uighur Congress.
"They poked a wire through his penis," Raxit says, citing the case of a Uighur wrongly accused of separatism who fled to Turkey recently after release from 18 months' imprisonment.
While the government doesn't necessarily order violence be used in most prisons, it encourages it in the case of Uighurs and believers of the banned Falun Gong spiritual group, activists say.
"In Xinjiang, the torture situation is particularly acute because there the Chinese government view [is] they do have a challenge, even more than Tibet," Becquelin says.
"Most of the guards are Han Chinese and these people are instructed all the time that we face a very serious challenge, that these people endanger national security. It's dehumanizing them as religious fanatics. All this encourages systematic violence," Becquelin says.
Since China banned Falun Gong in 1999, considering it the biggest threat to stability since the 1989 pro-democracy protests, many adherents have undergone torture in custody, the group claims.
While rights group believe Falun Gong sometimes exaggerate their claims, they and independent investigators agree violence is frequently used to force members to denounce their faith.
A Beijing lawyer, Gao Zhisheng, who recently carried out an investigation after his law firm received numerous reports of abuse, found ongoing "barbaric" persecution.
"They once kept me awake for 26 days. Whenever my eyelids closed for a second, they would beat me awake. I fainted several times," Gao quotes a retired school teacher "Liu Li" as saying.
Others went on hunger strike and were force fed until they coughed up blood.
A man named Wang Dejiang told Gao that police tied him to a wall heater with his toes barely touching the floor and left him there for hours, causing his legs to turn black.
"I can't describe the pain. I thought about committing suicide by biting my tongue, but they bound my mouth with more electrical wires until I couldn't move my mouth. I lost consciousness," Wang told him.
"To this day he can't walk properly," Gao says.
RSS