LONDON: Donor nations pledged on Thursday to give $11 billion in aid to Syrians by 2020 as world leaders tried to tackle the world's worst humanitarian crisis, while Turkey reported a new exodus of tens of thousands fleeing air strikes.

With Syria's five-year-old civil war raging and another attempt at peace negotiations called off in Geneva after just a few days, a donor conference in London sought to address the needs of some 6 million people displaced within Syria and more than 4 million refugees in other countries.

Underlining the desperate situation on the ground in Syria, Turkish Prime Minister Ahmet Davutoglu told the meeting that up to 70,000 Syrians were on the move towards his country to escape aerial bombardments on the city of Aleppo.

Davutoglu accused Syrian President Bashar al-Assad's forces, backed by foreign fighters and Russian air strikes, of seeking to do the same to Aleppo as they did to the besieged town of Madaya, where dozens have starved to death.

"What they want to do in Aleppo today is exactly what they did in Madaya before, a siege of starvation," he told a news conference at the end of the event.

Turkey is already hosting more than 2.5 million Syrian refugees. Jordan and Lebanon are the other countries bearing the brunt of the Syrian refugee exodus.

British Prime Minister David Cameron said donors had pledged a total of $6 billion for Syrians for 2016, and a further $5 billion to be spent by 2020, describing the total as the largest amount ever raised in a single day for a humanitarian crisis.

UN agencies are appealing for $7.73 billion for this year, with governments of countries in the region asking for an additional $1.2 billion for their national response plans.

"We have combined a renewed effort to address the shortfall in humanitarian funding with a new approach to provide the education and jobs that will bolster stability in the region," Cameron said.

Jordan, Lebanon and Turkey, where a significant share of the money pledged will be spent, committed to ensuring all refugee children in their countries would have access to education, and to opening up their economies so adult refugees could work.

"EATING GRASS"

Such measures are seen as crucial by European countries keen to improve living conditions for refugees in the region so they are less likely to travel to Europe.

A million migrants and refugees from Syria and other countries in the Middle East, Africa and Asia arrived on the continent last year, triggering a huge political crisis in the European Union.

Cameron said the international community would help the three main refugee host countries to meet their commitments on jobs and education, including with $40 billion of loans from financial institutions and the opening up of European markets.

"As a result there will be over 1 million new jobs in the region for refugees and residents alike," he said.

German Chancellor Angela Merkel, who is under intense pressure at home after a massive influx of refugees last year, said the EU would consider trade preferences for the host countries.

The almost five-year-old conflict has killed an estimated 250,000 people and stoked the spread of Islamist militancy across the Middle East and North Africa.

"With people reduced to eating grass and leaves and killing stray animals in order to survive on a day-to-day basis, that is something that should tear at the conscience of all civilized people and we all have a responsibility to respond to it," US Secretary of State John Kerry told the conference.

A UN envoy halted his attempts to conduct Syrian peace talks on Wednesday after the Syrian army, backed by Russian air strikes, advanced against rebel forces north of Aleppo, choking opposition supply lines from Turkey to the city.

Kerry told the conference he had spoken to his Russian counterpart Sergei Lavrov about the situation.

"We have agreed that we are engaged in a discussion about how to implement the ceasefire specifically as well as some immediate, possible confidence-building steps to deliver humanitarian assistance," he said.

In one of several blunt attacks on Russia during the day, Davutoglu said those supporting Assad's forces were committing war crimes and called on the United States to adopt a more decisive stance against Moscow.

Russia said it had serious grounds to suspect Turkey was preparing a military incursion in Syria, an accusation dismissed by a senior Turkish official as Russia trying to divert attention away from its own crimes in the country.