New York City, NY (AP) - Standard & Poor's warned Wednesday that Warren Buffett's bid for Burlington Northern Santa Fe Corp. could sap the liquidity and capital position of the legendary investor's insurance operations at Berkshire Hathaway Inc. and that jeopardizes the company's AAA rating.

The ratings agency placed it's ratings on Berkshire Hathaway on CreditWatch with negative implications following Berkshire's announcement Tuesday that it will buy Burlington Northern for $26.3 billion.

Standard & Poor's said it expects a significant part of the cash portion will come from Berkshire Hathaway's core insurance operations and the transaction will reduce the liquidity and "capital adequacy" of the company's insurance operations.