NEW YORK (Bloomberg) — Maurice (Hank) Greenberg, ousted as chief executive officer of American International Group Inc. two years ago, began a campaign to shake up the insurer's management after the stock fell 18 percent this year.

Greenberg, 82, AIG's biggest shareholder, is seeking talks with other investors to address concerns about leadership, the possibility of selling units and the company's stock performance, he said on Friday in a filing. Shares of AIG, the world's largest insurer, rose as much as 5.2 percent in extended trading.

"If he finds enough allies, Mr. Greenberg's initiative may give him a way to reassert influence on the company he built," said Donald Light, analyst at Celent LLC, a Boston-based financial research firm, in an e-mail.

Greenberg controls about 300 million AIG shares through C.V. Starr & Co., Starr International Co. and his personal holdings, according to Bloomberg data. AIG's board forced his retirement in March, 2005 two months before then-New York Attorney General Eliot Spitzer sued the company in an accounting probe.

"AIG has made tremendous progress over the past two and a half years and has established a strong culture of good corporate governance," said spokesman Chris Winans. "The company is pursuing the right strategies, and the board and management are united in their commitment to building shareholder value."

Greenberg's spokesman Ken Frydman declined to comment.

"There are opportunities to significantly improve" AIG's performance, Greenberg said in the letter. The company, which has lost about $32 billion in market value this year, fell 17 cents to $59.12 in New York Stock Exchange composite trading today.

"It's a huge company, it would be hard to sell it," said David Dreman of Dreman Value Management. "It would be a very bad time to sell a financial company."