Beijing  - China's Ministry of Public Security has launched a three-month campaign to eliminate "unnatural deaths" in prisons following several alleged beatings to death by guards, one of which prison staff claimed was caused by the prisoner's own nightmare, state media said on Thursday.

The ministry posted a notice on its website ordering all prisons and detention centres to learn from the case of Li Qiaoming, a man who was beaten to death in February by other prisoners at a detention centre in the south-western province of Yunnan.

The detention centre in Yunnan's Jinning county initially claimed that Li, 24, died accidentally during a game of hide-and-seek.

Staff at another detention centre in Jiujiang city in the eastern province of Jiangxi came up with an even more implausible explanation for the death of 50-year-old Li Wenyan, saying he died during a nightmare, the official People's Daily newspaper and other state media reported

At least three other suspicious deaths in custody were reported over the last month, including two minors who died within four days of each other at a juvenile detention centre in the central province of Hunan.

The ministry ordered local public security offices to "boost professional ethics, law awareness and respect for human rights" at prisons and detention centres.

"Officials should be brave to reveal their problems in the management of prisons and detention centres, and should exert doubled efforts to address them," it said.

Law professor Fan Chongyi told the official China Daily that the ministry's campaign did not go far enough.

"It aims to improve the police officers' professional awareness and regulate their behaviour, but in order to strike at the root of the problems, the detention houses should be put into the hands of an independent department," Fan told the newspaper.

Rights groups say the use of violence and torture by Chinese public security staff remains common, but the government says it is trying to address the problem.

In one high profile case, a court in the north-western province of Gansu sentenced two former police officers to 10 and eight years in prison in 2007 after convicting them of torturing to death a suspected rapist in 2004.

After his first visit to China in December 2005, the United Nations' special investigator on torture concluded that, despite some improvements in urban areas, torture remained widespread in China. (dpa)