WARREN BUFFETT is to be questioned early next week by the US Securities and Exchange Commission and Eliot Spitzer, the New York attorney-general, in an investigation into questionable insurance deals struck at companies run by the “Sage of Omaha”.

Berkshire Hathaway, Mr Buffett’s holding company, confirmed in a regulatory filing last night that several directors had been asked to appear before the investigators next week.

Regulators “have jointly interviewed a number of current and former officers and employees of General Re and General Reinsurance, and have indicated they plan to interview additional such individuals,” Berkshire said.

The Times has learnt that Mr Buffett will not be required to take an oath and has not been subpoenaed to appear. “He will appear voluntarily,” an SEC source said.

It is understood that representatives of the SEC, Mr Spitzer’s office and possibly the US Justice Department will be present throughout the interview. Mr Buffett will be asked about a $500 million insurance deal between General Re, one of Berkshire Hathaway’s insurance companies, and AIG, the insurance giant formerly run by Maurice Greenberg.

Mr Greenberg resigned as chief executive last month as questions mounted over the legality of its accounting methods. The investigators are examining whether AIG disguised hundreds of millions of dollars of loans as insurance policies to shore up its balance sheet.

AIG was forced to pay $850 million (£451 million) in January after its Marsh & McLennan brokerage unit was caught taking improper payments from insurers. The company admitted last week that its accounting methods may lead to more than $1.7 billion being wiped from its net worth.

Mr Buffett’s interview will come after reports that the star investor, famed for his stakes in companies such as Coca-Cola, has handed over documents related to the AIG deals.

It has been alleged that Mr Buffett drew the deals to the attention of investigators four months ago, when it became apparent that AIG’s accounting methods were under question. It is understood that when Mr Buffett handed over the documents in January he told investigators that he would co-operate with their inquiries.

A source close to the SEC said that Mr Buffett would not be treated any more favourably than any other witness. “The fact that he isn’t being questioned under oath means nothing,” the source said.

Mr Greenberg will be questioned next week. AIG would not comment.