US STOCKS-Futures turn lower after Fed cuts discount rate

(Updates with index futures falling)

NEW YORK, March 14 (Reuters) - U.S. stock index futures erased their initial gains and fell sharply on Sunday evening after the Federal Reserve unexpectedly cut the discount rate and said it will allow primary dealers on Wall Street to borrow at the discount rate.

S&P 500 futures SPc2 fell 20 points and Dow Jones industrial average futures DJc2 sank 142 points. Nasdaq 100 NDc2 futures tumbled 32.75 points. (Reporting by Chris Sanders; Editing by Tomasz Janowski)