Fed-watchers are awaiting the central bank's interest rate decision, due Wednesday. Expectations for a rate rise have significantly decreased over recent weeks, in part thanks to worse-than-expected non-farm payrolls figures for May.
Investors have been looking for safe haven as the chances of "Brexit" grow. 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.
No major economic data are expected.