Chinese President Xi Jinping "has built his anti-corruption campaign on an abusive and illegal detention system," said Sophie Richardson, China director for the Human Rights Watch (HRW).

In a report released on Tuesday, HRW claims widespread abuse within the so-called "shuanggui" branch of the Communist Party. In China, "shuanggui" stands for internal investigation and justice system used by the Party against 88 million of its own members. Many of them have faced accusations of graft since Xi came to power four years ago.

The system functions with no oversight from the state's judiciary. Typically, people subjected to "shuanggui" suddenly disappear and remain missing until they confess to corruption. They are later brought to court and convicted.

Chinese courts have a conviction rate of over 99.9 percent.

"The courts function as rubber stamps, lending credibility to an utterly illegal Communist Party process," said Richardson.

Beatings, hunger, and swollen feet

HRW analyzed 35 cases involving "shuanggui" for the report, basing its findings on interviews with survivors, lawyers and family members. Other sources included media accounts and court verdicts.

A Beijing-based lawyer said one of his clients was allowed an hour a sleep per day while under investigation. For the rest of the time, he was forced to balance a book on his head.

After eight days, he "confessed to everything and to whatever they said," the lawyer said. "At that point his feet were swollen like an elephant's and he could no longer urinate."

Other tactics used by the "shuanggui" officers include food and water deprivation, severe beatings, forcing prisoners into stress positions for extended periods of time and threats to family members, the HRW claims.

System to 'strike fear' across the party

A former detainee reported that he was made to stand and sit in alternating endless 12-hour shifts, saying: "My legs became swollen, and my buttocks were raw and started oozing pus."

Another suspect said he was forced to invent stories of his crimes. "They made me make it up. I had to make it up - if I didn't, they'd beat me," he said.

The threat of torture "strikes fear in the Party members regardless of their position," HRW said in the report. At least 11 people have died under "shuanggui" since 2010, according to the HRW report.

The system "not only facilitates serious human rights abuses, it depends on them," they added.

China did not immediately comment on the claims.

The parallel justice system has been increasingly criticized among China's legal community. Many claim the practice is unconstitutional and serves as a tool for political purges.

dj/kms (AFP, AP, Reuters)