Regulators are probing the accounting methods used by Warren Buffett's Berkshire Hathaway Inc., expanding an investigation that started with its connection to American International Group Inc.

Since January, authorities have been looking at whether Berkshire Hathaway's General Reinsurance Corp. unit helped AIG misstate financial results. Now, they are investigating how General Re and another insurance subsidiary performed accounting for a type of reinsurance that can be used to hide losses or smooth volatile shifts in earnings, Bloomberg reported.

“The accounting treatment applied by its own subsidiaries is being questioned,” Christopher Bebel, a former federal prosecutor who now practices law in Houston, told Bloomberg. “Berkshire Hathaway has always been viewed as a company that's above the fray and operates on a higher level.”

The new information was included in an Aug. 5 earnings report filed with the Securities and Exchange Commission. “The inquiries being made by the government relate to the investigation that commenced with the original subpoena received from the SEC on January 7, 2005, and are not as a result of any new investigation,” Berkshire Hathaway said in a statement.

The focus of the investigation had been on whether General Re helped AIG improperly book reinsurance, which allowed the country's largest insurer to overstate reserves by $500 million in 2000. Two former General Re executives pleaded guilty in June to federal charges of conspiring to violate securities laws.

"I suppose regulators are simply being thorough, and seeing if Berkshire accounted for something different from how its counterparties did," said Steven Check, who oversees $470 million at Check Capital Management Inc. in Costa Mesa, Calif., including $45 million in Berkshire shares, according to Reuters. "Warren Buffett has done things right for decades, so for me, the benefit of the doubt should go to him."

Among other regulators examining activities involving Berkshire units are federal prosecutors, New York Attorney General Eliot Spitzer and regulators in the UK, Australia, Canada, Germany and Ireland.

Berkshire also revealed that it fired a former reinsurance executive, Milan Vukelic, who had been under investigation by authorities overseas. Vukelic was head of the Faraday Group, a reinsurance brokerage unit in the UK, and led General Re's international reinsurance business.