The Supreme People's Procuratorate said during a video conference call on Friday that about half of the detainees had been beaten to death and blamed inadequate police supervision and negligence by prosecutors.

Of the 15 reported cases, seven died of beatings, three were classified as suicides, and two were described as accidents, procuratorate officials said. The three remaining cases were still under investigation.

Detention centers nationwide must have improved camera-monitoring systems installed, and they must be operational by September 30, the report said. The monitoring systems will be supervised by procuratorate officials to allow them to monitor the situation in the jails, public security ministry officials said last week at a meeting.

Meanwhile, China's public security ministry has launched a three-month investigation into conditions at detention centers after a spate of deaths at such institutions nationwide triggered public anger and also suspicion of law enforcement authorities.

At least six prisoners have reportedly died while in detention awaiting trial since Feb. 8, according to a China Daily report on April 14. The latest instance was early this month in Fuzhou, Fujian Province, in which drug addict Chen Hongqiang was found dead in a detention house, Xinhua reported. Chen had been sentenced to 10 days in detention for drug use.

Twenty-four-year-old Li Qiaoming's death at the Jinning detention house in Yunnan province in February was the first such case to be brought to the attention of the public. Li, who allegedly died during a "hide-and-seek" game on Feb. 8, was later found to have been beaten to death by three other inmates.

The incident triggered more media reports about similar suspicious cases, including that of 19-year-old Xu Gengrong, who died on March 8, the seventh day of his detention in Shaanxi Province.

Recently two minors reportedly died over four days at a provincial juvenile reformatory in Hunan Province, and 50-year-old Li Wenyan allegedly died in the middle of "a nightmare," according to a detention department head in Jiujiang of Jiangxi Province.