Stock index futures extended losses on Friday as the U.S. dollar's rebound pressured global commodity prices and weighed on natural resources shares.

The dollar rose broadly after Federal Reserve Chairman Ben Bernanke said monetary policy might have to be tightened as a recovery takes hold.

S&P 500 futures dipped 3.50 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures shed 28 points, and Nasdaq 100 futures fell 8.50 points.

U.S. front-month crude slipped 60 cents to $71.10 a barrel, while gold eased after hitting records for three straight sessions.

(Reporting by Ellis Mnyandu; editing by Jeffrey Benkoe)