Earlier on Wednesday, International Energy Agency's chief economist Fatih Birol also said that he expects prices - hovering at April 2009 lows - to rebound later this year.

President Petro Poroshenko said on Wednesday more than 9,000 Russian troops were backing Ukrainian separatist fighters that Moscow will be under pressure to reel in at high-stakes peace talks in Berlin.

Financial markets have been obsessing for months about the timing, size and structure of a European Central Bank bond-buying programme that seems likely to be unveiled today.