World leaders have opened a donor conference in London with an urgent plea for billions of pounds in aid for refugees from war-torn Syria."There is a critical shortfall in life-saving aid," said UK Prime Minister David Cameron, reports BBC.Germany pledged $2.6bn (£1.9bn; €2.3bn) and the UK $1.7bn in new refugee aid.However, the conference has been overshadowed by the suspension of peace talks in Geneva on Wednesday, and intense fighting on the ground.A Syrian government offensive, backed by Russian air strikes, is continuing north of Aleppo.Turkish Prime Minister Ahmet Davutoglu said an estimated 70,000 Syrians fleeing the bombing were moving towards Turkey.