WASHINGTON, Nov 15, 2007 (AFP) - The Federal Reserve injected 47.25 billion dollars into US money markets Thursday to help ease tight liquidity, the central bank said.

The Federal Reserve Bank of New York said it had injected the money in three separate operations: 19.25 billion dollars in a one-day operation, 20 billion dollars in a six-day operation and eight billion dollars in a 14-day operation.

The US central bank typically buys billions of dollars worth of securities from major banks, pumping extra cash into the banking system, which the banks are obliged to repurchase at a later date.

The New York Fed, which conducts the operations, has injected hundreds of billions of dollars into the financial system since early August, when credit flows seized up due to problems linked to the distressed US mortgage market.