The European Central Bank on Thursday said it would extend its massive bond-buying scheme until December 2017, stepping up its stimulus efforts to boost the eurozone's still fragile recovery.

The extension of the cash-pumping scheme was widely expected, but the bank surprised observers by saying it would lower the monthly purchasing amount to 60 billion euros ($65 billion) from 80 billion euros currently a month from April.

The bank's governing council also voted to keep key interest unchanged at record lows at their last policy meeting of the year, a spokesman said.