NEW YORK (Bloomberg) ? American International Group Inc.'s Maurice (Hank) Greenberg, who stepped down as chief executive of the world's biggest insurer this week, told employees to be proud of the "close-knit" company he's led for 38 years.

"I do not know of any other company in the world with this cohesive culture," Greenberg, 79, wrote in a March 17 letter to employees. "This should be the accomplishment we all should be most proud of, and it is my strongest hope and expectation that it will continue."

Greenberg, who remains a non-executive chairman, relinquished the CEO role amid probes by New York Attorney General Eliot Spitzer and US regulators into reinsurance that may be used to manipulate earnings. Greenberg was replaced by Martin Sullivan, who has worked at AIG since 1971, mostly recently as co-chief operating officer.

"I will do anything I can to be of help to the company," Greenberg wrote in the letter, calling Sullivan an "exemplar of AIG values." AIG spokesman Chris Winans confirmed the letter's authenticity.

Spitzer and the Securities and Exchange Commission are examining whether AIG initiated a reinsurance transaction with Berkshire Hathaway Inc.'s General Reinsurance unit four years ago to boost reserves for claims, said two people familiar with the probes. General Re CEO Joe Brandon declined to comment.

New York-based AIG replaced Chief Financial Officer Howard Smith and put Christian Milton, a vice president for reinsurance, on leave amidst the probes. The company delayed filing its annual report to regulators to review accounting for transactions under investigation.

AIG shares fell $1.04, or 1.7 percent, to $59.76 in New York Stock exchange composite trading. The shares have fallen 6.4 percent since the company said March 14 it would delay the filing.