Donor governments pledged Wednesday less than half the money the United Nations had been seeking to alleviate a worsening crisis in Syria, where it says nearly half the population is in urgent need.
The donors' conference in Kuwait came as preparations intensified for a UN-led peace conference in Switzerland next week that the main exiled opposition alliance has yet to commit to attend.
US ambassador to Syria Robert Ford was back in Istanbul lobbying opposition leaders to attend the long-delayed peace talks on which international hopes of ending the nearly three-year conflict are pinned.
UN chief Ban Ki-moon had issued an urgent appeal to donor governments for assistance for the millions of Syrians driven from their homes by a conflict that has killed more than 130,000 people and displaced millions.
"Half of the total population of Syrian people, nearly 9.3 million individuals, urgently need humanitarian aid," Ban said.
But at the conclusion of the conference, attended by delegates from nearly 70 nations and 24 international organisations, the UN chief was able to report pledges of just over $2.4 billion .
The UN was seeking $2.3 billion to support 9.3 million people inside Syria and $4.2 billion for refugees, expected to nearly double to 4.1 million in number by year's end.
UN Emergency Relief Coordinator Valerie Amos said there was particular concern for the plight of civilians trapped in enclaves besieged by the army or the rebels.
"I am deeply troubled by the persistent reports of people running out of food in those besieged communities, where some 245,000 people live," Amos said.
According to aid agencies, 10.5 million Syrians have no reliable source of food, more than a million children under five suffer from acute or severe malnutrition, about half the population has no access to adequate water or sanitation and 8.6 million have insufficient access to healthcare.
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US Secretary of State John Kerry, who attended the donors' meeting and announced an additional $380 million in US humanitarian aid, held telephone talks with his Russian counterpart Sergei Lavrov ahead of the Geneva II peace conference the two governments are jointly sponsoring.
Kerry will lead the US delegation but the main opposition alliance Washington has backed -- the National Coalition -- has put off until Friday its final decision on whether to attend, or stay away as key leaders have demanded.
"We're operating under the assumption that they will go. I don't want to venture to guess what would happen if they don't," State Department deputy spokeswoman Marie Harf said.
"It's not just that it's in our interest; it's that it's in their interest and the Syrian people's interest that they go."
Harf said a lot of behind-the-scenes meetings were already taking place to "create a climate" to give "more of a chance of success" to Geneva II, which aims to put in place a process for a transitional government to replace President Bashar al-Assad.
Washington has denied reports that it has threatened the Coalition that it will withdraw its support if it stays away from the peace conference.
But the opposition alliance's claim that it provides the only middle ground between Assad and Al-Qaeda have looked increasingly hollow as its fighters have been forced to look to hardline Islamists in an intensifying turf war with the jihadist Islamic State of Iraq and the Levant (ISIL).
ISIL has recaptured the city of Raqa, northeast of Damascus, the only provincial capital outside the control of Assad's forces, despite the mainstream Free Syrian Army enlisting the support of Al-Qaeda loyalists of the Al-Nusra Front against them.
And on Wednesday, at least one suspected ISIL suicide bomber struck a rebel checkpoint in the battleground northern town of Jarablos, killing 26 people, including at least three civilians.
The rebels' inability to best the jihadists on the battlefield has been a major factor in a Western drive for a diplomatic solution and has prompted calls for a policy rethink even from neighbouring Turkey, their key rear base.