The United Nations on Monday appealed for a record $12.9 billion in emergency aid, half of which is for victims of Syria's war, which is expected to generate another two million refugees next year.
The appeal came as dozens of people were reportedly killed in Aleppo when regime warplanes dropped barrels packed with explosives on rebel-held districts of the northern city, a focal point of the 33-month war.
The Syrian Observatory for Human Rights said 76 people died Sunday, among them 28 children, in the highest toll for air raids since the war started, while 10 others, including four children, were killed by the same weapons on Monday.
A fifth child was killed Monday when a shell struck a school in a regime-held neighbourhood, said the Britain-based Observatory, which relies on activists and medics on the ground for its reports.
The UN's humanitarian agency OCHA, which launched the appeal for emergency aid, said the funds are needed for 2014, when the number of Syrian refugees in the Middle East will nearly double to exceed four million.
Aid will also be needed for another 9.3 million people inside the war-ravaged country, it said.
"This is a tragedy," lamented Antonio Guterres, who heads the UN refugee agency UNHCR. He described Syria's war and its regional impact as "the most dangerous crisis for global peace and security since World War II."
The UN's World Food Programme said that almost half Syria's population of 23 million "is food insecure" while nearly a third "need urgent, life-saving food assistance."
It echoed the assessment of other organisations on the plight of Syrians inside the country and in refugee camps across the Middle East, which have been battered by inclement weather over the past week.
The International Rescue Committee, an NGO, said the price of bread in Syria has soared by 500 percent since March 2011, while the cost of blankets, at $27, is prohibitively high, amounting to "93 percent of the average monthly income."
More than 126,000 people have been killed in the war pitting forces loyal to President Bashar al-Assad against rebels fighting to topple his family's four-decade-old regime.
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Around 2.4 million refugees have already fled, mainly to Lebanon, Jordan, Turkey, Iraq and Egypt.
'Worst crisis' in decades
The strain on countries hosting refugees is projected to worsen next year, with OCHA now predicting the number of refugees will nearly double to 4.1 million in 2014.
OCHA said it and other international aid agencies and organisations would need a record $12.9 billion to help some 52 million people affected by 17 major crises around the world in 2014.
Nearly half of that amount will go to the Syrian conflict, with $2.27 billion needed for aid inside Syria and $4.2 billion needed for the refugees and their host communities in the region.
WFP said it was stepping up food aid next year and would also provide supplements to around 240,000 toddlers aged 6-23 months, to ensure they do not suffer from malnutrition.
"This is the worst humanitarian crisis that we have seen in decades, with every day more vulnerable Syrians pushed into hunger," said WFP Syria emergency coordinator Muhannad Hadi.
The opposition Syrian National Coalition meanwhile accused the Assad regime of deliberately targeting civilians with the explosive barrel attacks.
The regime "is trying, through a savage campaign against Aleppo, to take revenge and spread chaos in civilian areas" of rebel-controlled zones, it said.
The UN Children's Fund also condemned the attacks, with regional director Maria Calivis saying "it is absolutely unacceptable for children to be targeted in this manner."
In a separate development, the family of prominent human rights lawyer Razan Zaitouneh, who was kidnapped last week along with her husband and friends in rebel-held Douma, appealed for their release.
No party to Syria's conflict has claimed responsibility for their abduction. Zaitouneh is a well-known Syrian activist who was among the 2011 winners of the European Parliament's human rights prize.