Ex-security chief Zhou Yongkang, the most senior Chinese official to be investigated for corruption, has been arrested and expelled from the Communist Party, state media report.
The Supreme People’s Procuratorate, China’s top prosecuting body, said it had opened a formal probe against him.
Before he retired two years ago, Mr Zhou was the head of China’s vast internal security apparatus.
Many of his former associates and relatives also face corruption probes.
Since coming to power, Chinese President Xi Jinping has launched a high-profile campaign to weed out corruption among party and government officials.
Mr Zhou was accused of several crimes, including “serious violations of party discipline”, “accepting large sums of bribes”, “disclosing party and state secrets” and “committing adultery with several women” as part of corrupt transactions, Xinhua news agency reported (in Chinese).
Mr Zhou’s arrest was announced in a statement by the Supreme People’s Procuratorate, released late on Friday night.
Mr Zhou, who is in his 70s, has not been seen in public for more than a year.
Analysts say the investigation against Mr Zhou allows Xi Jinping to consolidate his power base, remove people opposed to his reforms, and improve the image of the Communist Party.
Mr Zhou was previously also a member of China’s top decision-making body, the Politburo Standing Committee.