Asian stocks hit 20-month lows, S&P futures slide as investors flee risk

In currency markets, the euro fell, extending weakness after European Central Bank President Mario Draghi said the bank's 2.6 trillion euro ($2.96 trillion) asset purchase program will end this year and interest rates could rise after next summer, despite fears about the monetary union's economic and political future.

The single currency was 0.1 percent lower at $1.1363.

The dollar was off 0.2 percent against the yen at 112.18 . The dollar index, which tracks the greenback against a basket of six major rivals, was 0.05 percent lower at 96.633.

U.S. Treasury yields fell as equity markets plunged. The 10-year yield fell to 3.1018 percent compared with its U.S. close of 3.136 percent on Thursday.

Oil prices gave up ground, heading for their third weekly loss after earlier rising on signals from Saudi Arabia's energy minister that there could be a need for intervention to reduce oil stockpiles.

U.S. crude dipped 1.07 percent to $66.61 a barrel. Brent crude fell 0.83 percent to $76.25 per barrel.

Spot gold ticked up 0.07 percent to $1,232.44 per ounce. ($1 = 0.8794 euros)