Federal Reserve Chairman Ben Bernanke defended the central bank's plan to buy government bonds during a private gathering with U.S. senators, responding to several days of attacks from Republicans who say the Fed is causing inflation and weakening the dollar. The Fed chairman denied the U.S. was manipulating the currency through its plan to purchase $600 billion of U.S. Treasury bonds and pointed to research by the Federal Reserve Bank of Boston which estimated the program could create 700,000 to one million jobs over two years.