Former security chief Zhou Yongkang is suspected to have established close connections with other allegedly corrupt officials, according to a magazine website report. Zhou allegedly formed links with Xu Caihou, the former vice-chairman of the Central Military Commission, and Ling Jihua, former minister of the United Front Work Department of the Communist Party of China Central Committee, the Caijing.com.cn report said.
Xu died of bladder cancer on Sunday.
"Zhou allegedly abused his power to establish close political and economic interests with other corrupt officials, including Xu Caihou, Ling Jihua, Bo Xilai, the former Party chief of Chongqing, and Li Dongsheng, the former vice-minister of public security, who secretly formed factions," the report said.
In addition, the former high-ranking officials, or "tigers", allegedly abused their powers to gain benefits for some enterprises and other concerns and also accepted huge bribes, according to the report.
Zhou Ruijin, former deputy editor-in-chief of People's Daily, said, "In recent days, a number of graft issues have tended to become family-, faction- or group-oriented," adding that the Zhou Yongkang graft case has involved many corrupt officials who allegedly formed a "huge corruption network".
Zhao Hongzhu, deputy head of the Central Commission for Discipline Inspection, said that no matter who is involved, officials suspected of corruption will be investigated thoroughly.
Since 2012, when China's new leadership took office, President Xi Jinping has carried out a widespread campaign to fight graft.
To date, more than 90 high-ranking officials, including 63 at ministerial level or above, and 30 generals in the military have been placed under investigation for suspected "serious disciplinary violations", a term frequently used to mean corruption.
Zhou Yongkang is the highest-ranking official investigated in the fight against corruption since 1978, when China's reform and opening-up was launched.
In July, Zhou, who retired from the Politburo Standing Committee in 2012, was placed under investigation for suspected serious disciplinary violations by the Central Commission for Discipline Inspection.
He was arrested in December, expelled from the Party and placed under investigation by the top prosecuting department, accused of a series of offences, including accepting bribes and leaking State secrets.
Zhou Qiang, chief judge of the Supreme People's Court, said: "After prosecuting him, the court will handle Zhou's case in accordance with the law. No one is above the law."
At a recently concluded meeting of the disciplinary commission in Beijing, Xi said the fight against corruption is "a matter of life and death" for the Party and the country.
"All Party members should consider the laws and Party disciplines as top priorities and behave appropriately to build a clean government," he said.
Xu Jinhui, director of the Anti-Corruption and Bribery Department under the Supreme People's Procuratorate, said investigations have shown that mineral resources, land transfers, bidding for development projects and law enforcement have become the worst-hit areas for corruption.
The downfall of a number of officials in some places, including Shanxi, Sichuan and Yunnan provinces, in the latest crackdown against corruption has been likened to "earthquakes". There are still 300 vacant positions for new government officials in Shanxi.
The commission said it will attach great importance to investigating officials who continue to act corruptly or are involved in "low moral activities". Other targets will include officials involved with "political and economic cliques" and those with poor reputations, it said.
Zhou Ruijin, the People's Daily former deputy editor-in-chief, said, "The fundamental problems in corruption cases are officials abusing their powers and the lack of a regular mechanism to supervise them."
Chen Xu, chief prosecutor at the Shanghai People's Procuratorate, said the premise behind the fight against graft is the correct supervision of officials through regulations that will prevent them from abusing their powers.
"It's more than necessary to draw up a special law that will provide a legal basis for the country to eliminate corruption at its roots," he added.