BEIJING (Reuters) - Suspects held under a controversial new detention measure introduced nation-wide by China’s anti-graft super ministry this year must be well treated, the corruption watchdog said on Thursday.

China’s rubber-stamp parliament, the National People’s Congress, finalised in March the establishment of a National Supervision Commission with the power to investigate all state employees, expanding the power of the existing regulator that had previously focused on Communist Party members.

The powerful new body has been criticized by some legal scholars for failing to protect the rights of suspects during investigations, in part because it will use a controversial “liuzhi”, or detention, system that operates outside existing criminal procedure law.

President Xi Jinping launched a sweeping campaign against deep-seated corruption more than five years ago. There have been several high-profile cases of graft suspects being mistreated or tortured, which the government has vowed to root out.

The graft-fighting Central Commission for Discipline Inspection outlined new rules it said made clear that the new detention method was not to be abused and acknowledged public concern.

“‘Liuzhi’ is an important investigation method granted by law to the supervision organs, and is a focus of high attention from various sectors of society,” it said in a statement on its website.

“On this, the rules are clear, that the ‘liuzhi’ method should be cautiously used under legal stipulations and the process strictly grasped,” the watchdog said.

There must also be no covert use of “liuzhi”, it said.

People who are investigated using this method must have their access to food and drink, rest and medical treatment guaranteed, the statement said.

The new rules also cover the questioning of witnesses.

Witnesses must be shown a document that outlines their rights and obligations when first being questioned, confidentiality must be kept and protection provided if they are at risk of “revenge attacks”, it said.

Xi announced the new detention system in October to replace the previous “shuanggui” system, in which party members submitted to questioning at a location and time chosen by investigators.

Rights groups have said the old secretive extra-legal measures that made use of off-grid locations with little oversight allowed torture, abuse and forced confessions.

Some rights activists and legal scholars have expressed concern the new detention system will merely entrench and extend previous practices under a veneer of legality. The government has denied this.