US Federal Reserve chairman Ben Bernanke said Friday that the Fed is ready to provide additional monetary accommodation if the economic outlook continues to worsen.

“The committee is prepared to provide additional monetary accommodation through unconventional measures if it proves necessary, especially if the outlook were to deteriorate significantly,” Bernanke said at the Fed annual retreat in Jackson Hole, Wyo.

Those “unconventional measures” might include relaunching the large-scale purchases of Treasury bonds and Mortgage-backed securities (MBS), tools the Fed used during the financial crisis and economic recession to inject more liquidity to the market and bring down interest rates.

In 2009 and early 2010, the Fed bought up 1.25 trillion dollars in mortgage securities and 175 billion dollars in debt from Fannie Mae and Freddie Mac, as well as 300 billion dollars of government debt, in an attempt to drive down mortgage rates and long-term Treasury yields.

The Fed had already made a small shift in the direction of a new round of asset purchases as it gathered Aug. 10 to discuss monetary policies.

After the meeting, the Fed announced decisions to buy more Treasury securities and keep its holdings of securities unchanged instead of letting them shrink as previously planned.

Despite the chairman’s reassurances of further stimulus, investors are still struggling to find clues, if any, as to what will trigger the approach.

“At this juncture, the committee has not agreed on specific criteria or triggers for further action,” Bernanke said.

He said the U.S. economic recovery and job creation were weaker than expected, but still held to the prospect that economic growth would pick up in 2011.

Bernanke’s remarks came just more than an hour after the government announced a significant downward revision of economic growth in the second quarter.

Growth was revised downward to an annual rate of 1.6 percent in the quarter ended in June, compared to the initially estimated pace of 2.4 percent, the Commerce Department reported. That was the slowest quarterly growth since U.S. economic activitys began to pick up in the second half of last year.