BEIJING (AP) -- The vice chairman of China's biggest state-owned energy company has become the latest prominent executive targeted by Communist Party investigators in a spreading anti-corruption campaign.

Liao Yongyuan, vice chairman of PetroChina Ltd., is under investigation for possible "serious violation of the law," the ruling party's Central Commission for Discipline Inspection announced late Monday. Its one-sentence statement gave no details but a separate statement by PetroChina said Liao was suspected of violating discipline, the party's term for corruption.

PetroChina is a key target of an anti-corruption campaign led by President Xi Jinping that appears to be aimed at tightening the party leadership's control over politically influential and often independent-minded state industries.

The state-owned oil and gas industry was a power base for Zhou Yongkang, the ruling party's former security chief who was arrested in December on charges including bribery and leaking state secrets. Control over state companies can provide political figures with jobs to reward supporters and money to promote their own careers.

PetroChina is Asia's biggest oil and gas producer by volume but is regarded by executives at other companies as bloated and inefficient.

Its vast cash flow and the complexity of its heavily regulated and politically sensitive industry create ample opportunities to divert money or assets to private use.

At least four present and former executives of PetroChina and its parent, China National Petroleum Corp., have been detained. A former CNPC chairman was fired in September as head of the Cabinet body that oversees China's biggest state-owned companies.

Zhou, who stepped down in 2012 as a member of the party's ruling inner circle, the Standing Committee, would be the highest-ranking Chinese political figure to be prosecuted since the early 1980s. He is a former CNPC general manager.

Liao spent most of his career at PetroChina, working in Gansu province in the northwest and Sichuan in the southwest before becoming its vice president in 2005, according to the company website.