S&P 500 stock index futures extended losses on Friday on caution over how long the market's recent run-up would last, following General Electric Co and Bank of America Corp quarterly results.

The bar for expectations is higher, and that's one of the reasons I'm not seeing an explosive move here pre-market, said Craig Peckham, equity trading strategist at Jefferies & Company in New York. It's going to be hard to add onto the big gains we've had this week.

In Thursday's trading Wall Street held to a fourth-straight day of gains.

S&P 500 futures were 4 points lower 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 fell 6 points, and Nasdaq 100 futures shed 1.75 points.

(Reporting by Ellis Mnyandu; Editing by Padraic Cassidy)