SHANGHAI • The president of one of China's "big four" banks has resigned for personal reasons, the company said, after reports said he had been taken away in a corruption investigation, as probes widen in the country's financial sector.

Mr Zhang Yun had stepped down from state-owned Agricultural Bank of China, the bank said in a statement to the Hong Kong stock exchange, where it is listed.

The announcement came a month after China's news portal Sina reported that Mr Zhang, 56, had been taken away for questioning.

On Sunday, meanwhile, China's biggest brokerage, Citic Securities, told the Hong Kong Exchange it had lost contact with two members of its executive committee - Mr Chen Jun and Mr Yan Jianlin - and they might be assisting an investigation.

The Chinese authorities have launched a series of investigations into the financial sector after a debt-fuelled stock market bubble burst in the summer in a rout that wiped out trillions of dollars of market capitalisations.

Citic Securities said two weeks ago that the company itself was being probed by the market regulator, the China Securities Regulatory Commission, following police investigations into several company executives for insider trading and leaking inside information.

Separately, Xu Ming, a billionaire tycoon who testified that he paid former rising Communist Party political star Bo Xilai millions in bribes has died in prison.

Xu, 44, the chief accuser at the trial of the fallen Chongqing party chief, probably died of a "sudden heart attack" on Friday, the Xinhua news service said yesterday. He was due to be released in September next year.

AGENCE FRANCE-PRESSE