Berkshire Hathaway Incorporated said its chairman, Warren Buffett, was unaware of how American International Group Incorporated intended to use reinsurance transactions under investigation by American regulators and prosecutors.

Regulators are examining whether AIG, the world’s largest insurer, used the four-year-old agreements with Berkshire to manipulate its finances.

Mr. Buffett agreed to be interviewed by investigators, and several Berkshire executives have already answered questions, the Omaha, Neb.-based company said in a statement yesterday.

“Mr. Buffett was not briefed on how the transactions were to be structured or on any improper use or purpose of the transactions,” Berkshire said in the statement.

New York Attorney General Eliot Spitzer and the Securities and Exchange Commission are concerned that AIG may have used the deals with Berkshire’s General Re Corporation to make AIG’s reserves for claims appear larger, people familiar with the probe said. The investigation has since broadened to transactions with other reinsurers and prompted the resignation of AIG’s chief executive, Maurice “Hank” Greenberg.

Berkshire’s statement yesterday said a press report suggesting that Mr. Buffett was briefed on the “nature” and “structure” of the AIG deals was incorrect. Berkshire said it was cooperating with investigators and didn’t expect to restate its financial reports. Mr. Buffett’s interview is scheduled for April 11, people familiar with the probe said.

Shares of Berkshire rose $200, or 0.2%, to $87,000 in New York Stock Exchange composite trading. AIG shares rose 2.1% after Mr. Greenberg, 79, on Monday said he would step down as AIG’s chairman. He relinquished his CEO role two weeks ago after almost four decades at the helm.

The probe has shone an unwelcome spotlight on Berkshire and Mr. Buffett, who often uses his annual shareholder reports to encourage straightforward accounting and executive accountability among American companies. Berkshire is among the biggest sellers of the non-traditional reinsurance products that regulators are concerned might function as disguised loans, according to Fox-Pitt Kelton Incorporated analyst Gary Ransom.

“I’m surprised it took them this long” to question Mr. Buffett, said Jack Lake, an analyst at Victory Capital Management, which oversees $53.5 billion in Cleveland. “Berkshire is the counterparty of the AIG transactions.”

Victory’s parent, KeyCorp, owns at least $79 million worth of Berkshire shares.