WASHINGTON (Bloomberg) — Federal Reserve chairman Ben S. Bernanke said the use of credit default swaps to destabilise a country is "counterproductive," and added the central bank is reviewing the arrangements of Goldman Sachs Group Inc. and other companies with Greece.

"We are looking into a number of questions related to Goldman Sachs and other companies and their derivatives arrangements with Greece," Bernanke said today in testimony before the Senate Banking Committee in Washington.

Greek bonds slid yesterday, pushing the premium investors demand to hold the nation's 10-year securities instead of German bunds to the most in more than two weeks, amid concern the country's credit ratings may be cut.

Federal Reserve officials are using new supervisory powers over firms such as Goldman Sachs and Morgan Stanley to gather information on financial system risks. Bernanke was responding to a question from Senator Christopher Dodd, a Connecticut Democrat, who asked if there should be limits on the use of credit default swaps to prevent "runs against governments".

"Obviously, using these instruments in a way that intentionally destabilises a company or a country is — is counterproductive, and I'm sure the SEC will be looking into that," Bernanke said. "We'll certainly be evaluating what we can learn from the activities of the holding companies."

Moody's Investors Service said it may downgrade Greek debt. The Standard & Poor's 500 Index fell yesterday.

Goldman Sachs helped Greek officials raise $1 billion of off-balance-sheet funding in 2002 through swaps, which European Union regulators said they knew nothing about until recent days.

Goldman Sachs did "nothing inappropriate" when it arranged currency swaps for Greece that reduced the nation's national debt by 2.37 billion euros ($3.2 billion), a top executive said.

"They did produce a rather small, but nevertheless not insignificant reduction, in Greece's debt-to-GDP ratio," Gerald Corrigan, chairman of Goldman Sachs's regulated bank subsidiary, told a panel of UK lawmakers February 22. The swaps were "in conformity with existing rules and procedures".

"As a matter of policy, we don't comment on legal or regulatory matters," Michael DuVally, a Goldman Sachs spokesman, said today.

Corrigan is the former president of the Federal Reserve Bank of New York. The Federal Reserve gained oversight powers over Goldman Sachs and Morgan Stanley following their conversion to bank holding companies in September 2008.

Yields on two-year Greek bonds rose to the highest since February 9 after Standard & Poor's and Moody's said they may cut their ratings if Greece fails to implement a plan to reduce its budget deficit. Pierre Cailleteau, managing director of sovereign risk at Moody's, said a downgrade may come by the end of March.

"Greece is able to make headlines every day, and for now volatility is here to stay," said Michiel de Bruin, who helps manage $28 billion of assets as head of euro government bonds at F&C Investments in Amsterdam. "The market is also taking into account the possibility of a double dip in economic growth, and that's causing risk aversion."

The cost of insuring against default on Greek government bonds rose for a fourth day, with the credit-default swaps on the debt rising 10 basis points to 392, the highest in more than two weeks, according to CMA DataVision.