A former vice-governor of Sichuan province, who for years was the aide of the Communist Party's former top security official, has been placed under investigation. Guo Yongxiang, 64, chairman of the Federation of Literary and Art Circles in Sichuan, was being probed by the party's Central Commission for Discipline Inspection for serious violations of party discipline - a common euphemism for corruption - according to China Central Television, which cited unnamed sources within the top graft-busting agency. The semi-retired official appears set to be the sixth vice-ministerial-level official brought down since early December, following the downfalls of Liu Tienan, former deputy chief of the National Development and Reform Commission; Li Chuncheng, former deputy party secretary of Sichuan; Wu Yongwen, former deputy head of the People's Congress in Hubei; Yi Junqing, former director of the party's Central Compilation and Translation Bureau; and Ni Fake, former vice-governor of Anhui . As part of a nationwide graft-busting push, the party's general secretary, Xi Jinping, vowed in January to crack down on corrupt officials - regardless of whether they were high-ranking "tigers" or low-ranking "flies" - two months after taking over the top post from Hu Jintao . According to their official profiles, Guo and former security tsar Zhou Yongkang worked together for 12 years, until 2002, when Zhou became a member of the Politburo as head of the Public Security Ministry. In 1990, Guo was working at the Shengli Petroleum Administration Bureau, which was then affiliated with China National Petroleum Corporation (CNPC), of which Zhou had already been deputy chief for two years. And in 1998, when Zhou was promoted from general manager of CNPC to being the minister for land and resources, Guo followed him and worked as director of the ministry's general office. In 2000, a year after Zhou was appointed party secretary of Sichuan, Guo was named deputy secretary general of the provincial party committee under Zhou's leadership. Zhou became a member of the Standing Committee in 2007 and oversaw law enforcement. He retired after the 18th national congress in November.