Stock index futures fell sharply on Tuesday as a rise in European bond yields, including a jump in the Italian benchmark 10-year to above 7 percent, highlighted market fears that Europe's debt crisis was mushrooming into a wider systemic problem.

S&P 500 futures fell 15.5 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures slid 123 points, while Nasdaq 100 futures lost 32.75 points.

(Editing by Jeffrey Benkoe)