BEIJING (REUTERS) - The top political official of a major city in south-west China has been placed under official investigation, the country's graft busting agency said.

Yu Yuanhui, the Communist Party secretary of Nanning, capital city of the Guangxi Zhuang Autonomous Region, is being investigated for "severe disciplinary and law violation," a common euphemism for corruption, according to a statement by the Central Commission for Discipline Inspection.

Yu, who studied at Harvard University's Kennedy School of Government a decade ago, is also a member of the standing committee of the regional government.

China's President Xi Jinping has vowed to target high-ranking "tigers" as well as lowly "flies" in a broad campaign against corruption that has intensified over the last two years.

Jiang Jiemin, the former head of the CNPC, the country's top energy group, admitted guilt and asked for leniency at the opening of his trial last month on charges of bribery and the abuse of power.

Jiang was a close associate of Zhou Yongkang, the once-powerful domestic security chief and member of the elite Politburo Standing Committee, the most senior person to have been charged with corruption.