Stricter monitoring measures are being introduced in all Chinese jails after at least 15 people died in unusual circumstances this year alone, state media reported Sunday.

The Supreme People's Procuratorate said about half those detainees were beaten to death, blaming inadequate supervision of police and negligence by prosecutors, the Beijing Times reported.

Of the 15 reported cases, seven died of beatings, three were classified as suicides and two were described as accidents, procuratorate officials said on a videoconference call on Friday, according to the report.

The three remaining cases were still being investigated, it added.

Prosecutors were told that some of the deaths could have been prevented had they done their jobs properly, the report said.

China's public security ministry has launched a three-month investigation into conditions in detention centres in response to mounting public anger over the recent deaths, including those of three teenagers.

A public security ministry conference last week was told procurate officials would supervise the installation of improved camera monitoring systems in all detention centres and that they must be operating by September 30, the report said.

The systems would allow legal officials to directly monitor what goes on, the report said.

Earlier this month, the official Xinhua news agency reported that a drug addict serving a 10-day sentence was found comatose in his cell and died in hospital in the southeast city of Fuzhou.

Days before Liu Yushan, 35, died "suddenly" of possible heart problems in a Foshan city jail in southern Guangdong province. Another detainee died in the same city last month after he "fell off his bed and hurt his head," Xinhua reported.

Prosecutors have also accused police of torturing a teenager to death last month in north Shanxi province while trying to extract a confession, state media said.

Reports have also surfaced of two youths who died recently at a juvenile detention centre in central Hunan province. Their parents have said their large open wounds suggested they were victims of police brutality.