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.

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.

Focus on children

The goal of the donor conference is to raise $9bn (£6.2bn) for Syrian refugees.

The US pledged about $925m, most of it for life-saving assistance such as food and shelter.

Mr Cameron and UN Secretary-General Ban Ki-moon both spoke of the need to get all Syrian refugee children into education within months.

Sixty countries are represented at the conference, including 30 world leaders.

It is the fourth of its kind, focusing on education and jobs for the 4.6 million Syrian refugees in neighbouring countries. Turkey is hosting 2.5 million - the largest number.

Hours before the conference began, peace talks between the Syrian regime and opposition were suspended.

The United Nations-brokered talks, which opened just two days ago, are expected to resume on 25 February. Staffan de Mistura, the UN's special envoy at the talks, admitted there had been a lack of progress but said that the negotiations had not failed.

UN chief Ban Ki-moon said the talks were "undermined by the continuous lack of sufficient humanitarian access, and by a sudden increase of aerial bombings and military activities within Syria".

He urged the warring sides to "get back to the table, not to secure more gains on the battlefields".