The China National Petroleum Corporation (CNPC), Asia's largest oil and gas producer, confirmed on Thursday that it has decided to remove its four senior executives under investigation for "serious violations of discipline" from their posts.

The four executives are Wang Yongchun, deputy general manager of the CNPC; Li Hualin, deputy general manager of the CNPC; Ran Xinquan, vice president of PetroChina Company Ltd.; and Wang Daofu, chief geologist of PetroChina.

The CNPC's Communist Party of China (CPC) committee said the four have been relieved of Party-related posts and corporate administrative posts, and their job titles with the CNPC's joint-stock and listed subsidiaries will be removed following due procedures.

The CNPC has appointed Liu Hongbin, Wen Qingshan, Zhao Zhengzhang and Zhao Wenzhi to take over their positions.

On Monday, the CPC Central Commission for Discipline Inspection confirmed that then-CNPC deputy general manager Wang Yongchun is being investigated over suspected "serious violations of discipline."

The State-owned Assets Supervision and Administration Commission on Tuesday confirmed the other three are being investigated under the same allegation.

China's new leadership has widened its crackdown on corruption, netting a number of high-ranking and low-ranking officials over suspected legal and disciplinary violations.

In early July, former railways minister Liu Zhijun was given a suspended death penalty for bribery and abuse of power, making him the highest-ranking official sentenced for such offenses since the country's new leaders took office in March.

The extending list also includes Liu Tienan, former deputy director of the National Development and Reform Commission, who is being probed for bribe-taking, and Li Chuncheng, former vice secretary of the CPC Committee of Sichuan Province, who was sacked in December over suspected "serious disciplinary violations."

Some lower-ranking officials have also fallen amid the growing impact of social media whistle-blowing. Lei Zhengfu, a former official in southwest China's Chongqing Municipality embroiled in a sex video scandal, was sentenced to 13 years in jail for bribery in June.