Traders work on the floor of the New York Stock Exchange shortly after the opening bell in New York April 12, 2016. REUTERS/Lucas Jackson

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.