China National Petroleum Corporation has announced the discovery of more corruption cases among its top executives and pledged no respite in the fight against graft.

The corporation, which is the country's largest oil and gas producer and supplier, on Monday published a memo to its staff stating that all suspects involved in the corruption of Jiang Jiemin and Wang Yongchun, former top leaders of the company who are now in jail, would be dealt with impartially under the law.

Some of the unnamed suspects have been punished using Party disciplinary measures, while others have been referred to Party disciplinary departments for further investigation.

No further information about the suspects was available.

Jiang Jiemin, former chairman of the corporation, was arrested in 2013 shortly after leaving the company to head a government body overseeing state-owned companies.

He was charged with accepting bribes and abuse of power and in October was sentenced to 16 years in prison for taking bribes of around 14 million yuan ($2 million).

Meanwhile, Wang Yongchun, former vice general manager of the corporation, was given a 20-year sentence in October for?taking bribes of nearly 50?million yuan and abuse of power.