Chinese authorities began criminal investigations on Friday into three more former high-ranking officials over corruption allegations, all of them allies of powerful, retired domestic security chief Zhou Yongkang.
Sources have told Reuters that Zhou has been put under virtual house arrest while the ruling Communist Party investigates him for graft, though the party has made no announcement about his case.
Several of Zhou's political allies have been held in custody and questioned over corruption.
China's top prosecutor said that three of them - two former Zhou secretaries called Tan Hong and Yu Gang and a former vice governor of the southern province of Hainan called Ji Wenlin - were now formally being criminally investigated.
It added, in brief separate statements on its website, that all three were suspected of taking bribes and were in custody. No other details were provided.
It was not possible to reach any of them for comment.
Chinese media have linked all three with Zhou, though the prosecutor did not make that connection.
The prosecutor said on Monday that it had also begun criminal investigations into two other Zhou allies, former Vice Minister of Public Security Li Dongsheng and Jiang Jiemin, once the top regulator of state-owned enterprises.
As the wheels of Chinese justice can turn slowly, their trials may be a long way off. All will almost certainly be found guilty as Chinese courts are controlled by the Communist Party and will not challenge the party's allegations.
President Xi Jinping has launched a crackdown on deep-rooted graft since taking office last year, warning, like many before him, that the problem was so severe it could affect the party's ability to rule.