The U.S. Federal Reserve on Wednesday, in a surprise move, said it will buy up to $300 billion worth of longer-term U.S. government debt over the next six months and expand purchases of mortgage-related debt to help ease credit market conditions.

In these circumstances, the Federal Reserve will employ all available tools to promote economic recovery and to preserve price stability, the Fed said.

With benchmark rates virtually at zero, the Fed has turned its focus to pumping money into stressed credit markets in the hope of restarting lending and restoring growth -- a policy Fed chief Ben Bernanke has dubbed credit easing.

(Reporting by Mark Felsenthal and Alister Bull; Editing by Tim Ahmann)