Another senior executive at China National Petroleum Corporation (CNPC) has reportedly been asked to assist in the widening corruption probe into the state energy giant. The company is a power base of Zhou Yongkang, a former Politburo Standing Committee member and ex-security tsar who is rumoured to soon be named as the focus of an official graft investigation. Wen Qingshan, chief accountant at CNPC and a member of the state-owned enterprise's Communist Party committee, had been "summoned to assist the investigation" into the company graft case in "recent days", the influential Caixin.com reported yesterday, citing a source with CNPC. The investigation into senior officials at the company, where Zhou had once been general manager, was made public in August. Jiang Jiemin , who was at the time the head of the state enterprises regulator and also a ex-chief of CNPC, was also placed under investigation. Speculation intensified this month Beijing would make an announcement about Zhou soon. Wen was promoted to chief accountant in late July, according to company announcements, and later also appointed chairman of Kunlun Energy, a Hong Kong listed subsidiary under CNPC. Kunlun's previous chairman Li Hualin, also a CNPC deputy general manager, was one of the officials named in August. A CNPC spokesman did not immediately return calls.