The UN has appealed for $6.5bn (€4.7bn) for Syria and its neighbours to help 16 million people next year, many of them hungry or homeless victims of the 33-month conflict.
The Syrian appeal accounted for half of an overall funding plan of $12.9bn to help 52 million people in 17 countries, announced by UN emergency relief coordinator Valerie Amos at a meeting of donor countries in Geneva.
"This is the largest amount we have ever had to request at the start of the year," she told a news conference, referring to the worldwide appeal.
She said the money requested for Syria was the largest UN appeal ever for a single crisis.
"The increasing number of internally displaced people and refugees is generating greater needs across all sectors and straining the capacities of neighbouring countries, with profound regional consequences," the appeal said of Syria.
The UN sent its first delivery of humanitarian aid by air to Syria from Iraq yesterday.
It said it plans to deliver more food and winter supplies to the mainly Kurdish northeast in the next 12 days.
It is seeking $2.3bn to help 9.3 million people in Syria next year, compared with its 2013 appeal of $1.4bn, of which only 62% has been received, UN figures show.
For five neighbouring countries - Egypt, Iraq, Jordan, Lebanon and Turkey - the world body is seeking $4.2bn to assist up to 4.1 million Syrian refugees and host communities who will be given food aid, including cash or vouchers.
UN agencies aim to provide food, clean drinking water, shelter, education, health services and polio vaccines to Syrians inside and outside the devastated country.
The UN World Food Programme aims to feed 4.25 million people in Syria, where it reached only 3.4 million in November.
"This is the worst humanitarian crisis that we have seen in decades, with every day more vulnerable Syrians pushed into hunger," WFP's Syria Emergency Coordinator Muhannad Hadi said.
The overall UN appeal also includes aid to Sudan, South Sudan, Yemen, Democratic Republic of Congo, Afghanistan and the Philippines.