BEIJING (Reuters) - China has placed Mr Liao Yongyuan, a general manager of state-owned China National Petroleum Corporation (CNPC), under investigation for "serious disciplinary violations", usually shorthand for graft, the country's corruption watchdog said late on Monday.

China's Central Commission for Discipline Inspection (CCDI) gave no further details in a brief statement posted on its website (www.ccdi.gov.cn).

CNPC, China's biggest oil producer, is the parent company of PetroChina. The company could not immediately be reached for comment.

The graft watchdog said last month it had targeted 26 giant state-owned companies for inspections this year, including CNPC, the China National Offshore Oil Corp., and the China National Nuclear Corp. Several senior CNPC executives have already been put under investigation in a far-reaching corruption crackdown, among them former chairman Jiang Jiemin and the company's vice president, Wang Yongchun.

CCDI said on Sunday it had also put Mr Xu Jianyi, the chairman of one of the country's top state-owned automakers, the China FAW Group Corp, under investigation for "violating Party discipline".

After taking over as party and military chief in late 2012, President Xi Jinping declared war on corruption at all levels. Scores of senior officials have been brought down by the campaign, including former security tsar Zhou Yongkang.