Federal prosecutors are reported to have launched a criminal investigation into Maurice "Hank" Greenberg, chairman of American International Group, following allegations that he manipulated the insurance company's share price to save money on a big acquisition deal.

The Wall Street Journal reports that the inquiry by the US Attorney's office in Manhattan focuses on whether Greenberg violated criminal securities statutes shortly before AIG finalised its acquisition of insurer American General in August 2001, according to people close to the matter.