NEW YORK (Reuters) - U.S. stock index futures were lower in early trading, indicating Wall Street may open with losses on Monday, the first trading day after the worst mass shooting in U.S. history.

S&P e-mini futures <ESc1> were down 0.27 percent at 2090.50 after about 20 minutes of trading.

Earlier on Sunday, a man armed with an assault rifle killed 50 people at a packed gay nightclub in Orlando, Florida, which President Barack Obama described as an act of terror and hate.

(Reporting By Nick Zieminski in New York; Editing by Meredith Mazzilli)