US Federal Reserve chairman Ben Bernanke said on Friday that the economic recovery has weakened more than expected, and that the Fed is ready to take further steps if needed to spur growth.

Bernanke's comments, in an address to an annual conference of global central bankers held by the Fed, came as the government reported that economic growth in the second quarter was weaker than it had originally estimated.

With interest rates held at ultra-low levels since December 2008, the Fed has turned to other measures, pumping close to $1.7-trillion into the economy.

"The (Fed) is prepared to provide additional monetary accommodation through unconventional measures if it proves necessary, especially if the outlook were to deteriorate significantly," Bernanke told the Fed conference, held in Jackson Hole, Wyoming.

He added that the US central bank had not decided what would prompt additional easing.

"At this juncture, the committee has not agreed on specific criteria or triggers for further action," he said. Bernanke said the US central bank's purchases of longer-term securities have been effective in lowering borrowing costs and that he believes the benefits of buying more such assets, if needed, would outweigh any disadvantages.