Wall Street eyes Fed, Brexit as global markets slump

U.S. stock index futures indicated a lower open Monday, amid a wider "risk-off" move in global indexes, as investors looked ahead to crucial central bank decisions from the U.S. and Japan this week.

The Federal Reserve is not expected to take action at its rate decision Wednesday, but the actions of other central banks will likely continue to be felt as their easing programs wash over global bond markets. Sovereign yields have ticked lower recently as traders favor supposed safe haven investments over equities. The European Central Bank added corporate debt to its purchases in the past week, adding more downward pressure on yields.

Meanwhile in Asia, the Bank of Japan (BOJ) is also scheduled to hold a policy meeting on June 15 with analysts saying that that bank could surprise markets with additional easing this week.

Investors are also expected to remain skittish on the upcoming . A new poll published on Friday showed that the majority of Brits favor leaving the EU which is rattling markets.

"Momentum is behind the 'vote leave' camp as polls seem to show more support for Brexit than at any point in the campaign so far. We've seen heavy selling and shortened our Brexit market price from over 80 percent - implying a one-in-five chance of Britain leaving the EU – to 66 percent, which indicates a one-in-three chance of Brexit," Joe Rundle, the head of trading at U.K. spread better ETX Capital, said in a morning note.

The worst mass shooting in U.S. history is also likely to weigh on markets, as details unfold about the lone gunman responsible for the killings of at least 50 in a nightclub in Orlando, Fla. early Sunday morning.

European stocks traded sharply lower on Monday and in Asia, Japan's Nikkei 225 tumbled 3.51 percent as fresh strength in the yen pressured stocks, with major exporters selling off. U.S. stocks closed lower Friday, weighed by renewed global growth concerns.

There are no economic data due on Monday and no significant earnings reports expected in the U.S.

—CNBC's Patti Domm, Arjun Kharpal and Holly Ellyatt contributed to this article.