MANHATTAN, New York (Bloomberg) - American International Group Inc. (AIG), the world's largest insurer by assets, sued the company's former CEO Maurice "Hank" Greenberg, claiming he "misappropriated" AIG shares worth $20 billion.

AIG claims Mr. Greenberg and six other former executives, including ex-chief financial officer Howard Smith, misappropriated stock in AIG affiliate, Starr International Co., in 2005, according to a complaint filed late on Wednesday in New York state court in Manhattan.

AIG claims Mr. Greenberg, Mr. Smith and other defendants put themselves on Starr's board and converted a block of stock into a "private 'investment vehicle' for the benefit of Mr. Greenberg and the other defendants."

"This is a protective action to preserve our claims against these individuals personally," said AIG spokesman Christopher Winans.

Mr. Winans said Mr. Greenberg and the other defendants had refused to extend the three-year legal deadline for filing such a lawsuit based on alleged conduct in 2005.

Glen Rochkind, a spokesman for Starr International, said: "We expect to be successful in dismissing this additional merit-less lawsuit by AIG involving Starr International. This is little more than forum-shopping, since AIG's earlier lawsuit against Starr International has not been successful in federal court."