They said an eight-member team had left Beijing for Shanxi and Henan provinces, where workers as young as 8 were working in kilns, subjected to beatings and long hours with little food and no pay. The reports shocked the country and lead to accusations that local police and government officials were involved.
"Our attitude is very clear. If any malfeasance is found out in the police, we must deal with it severely," Wu Heping, spokesman of the Ministry of Public Security, was quoted as saying in the Beijing Daily Messenger newspaper.
He said anyone found sheltering or turning a blind eye to the illegal kilns would be disciplined or punished.
"The ministry will not cover up a single case," Wu said, according to the China Daily.
The official Xinhua News Agency reported Wednesday that the Supreme People's Procuratorate, China's top prosecutor, had sent two prosecutors to join a local prosecution team in investigating official negligence behind the forced labor scandal.
"Our past experiences have shown that dereliction of duty is always behind major accidents. Prosecutors should learn to investigate official negligence when major accidents are exposed by media," an official with the department that examines official dereliction of duty was quoted as saying.
China Daily said the police bureau in Hongtong County of Shanxi had admitted dereliction of duty by one officer, who was responsible for the security of Caosheng Village.
The officer had never visited the kiln in the village where, late last month, 31 workers were freed. One laborer had been nearly beaten to death, the newspaper said.
It said nearly 600 workers, including 51 children, had been freed after about 45,000 policemen raided more than 8,000 kilns and small coal mines in Shanxi and Henan provinces. About 160 suspects have been detained.
The use of slave workers came under the spotlight in part because of an open letter posted online signed by a group of 400 fathers appealing for help in tracking missing sons they believed were sold to kiln bosses.
The fathers accused Henan and Shanxi authorities of ignoring them or even protecting the kilns and human traffickers, saying about 1,000 children were being forced to work at kilns under conditions of extreme cruelty.
The state-run Xinhua News Agency said Wang Dongji, a Communist Party branch secretary at a village in Shanxi, was being investigated after his son was found to be an owner of a kiln where 32 people were starved, beaten and forced to work 14 hours or more a day.
Xinhua reported Wednesday that Xi'an, a major city in northwest China, had permanently closed 13 job agencies around its railway station that were allegedly deceiving rural workers and sending them to work in the illegal kilns in neighboring Shanxi.
"We will not allow any other job agency to open near the railway station in the future," Meng Zhe, director of Xi'an Railway Station Square Administration, was quoted as saying.