The Syrian appeal accounted for half of an overall funding plan of $US12.9 billion for 2014 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," Amos told a news conference, referring to the worldwide appeal.
The money requested for Syria, covering food, drinking water, shelter, education, health services and polio vaccines, was the largest UN appeal ever for a single crisis.
Well over 100,000 people have been killed in a civil war that has uprooted millions of people, devastated many cities and wreaked havoc on the economy and basic public services.
Syria's currency has plummeted by 80 percent since the revolt began in March 2011, and destruction of the water network has left 10 million people - almost half the pre-war population - relying on the United Nations to chlorinate water.
"There are parts of country where for 22-23 hours a day people aren't getting electricity. Fuel is scarce," said Amos, who visited Damascus briefly on Saturday to meet ministers.
"Even if the violence were to stop tomorrow we would have to maintain help on the humanitarian front," she said.
Amos was cautious about chances of a breakthrough at peace talks between President Bashar al-Assad's government and his opponents that are scheduled to begin in Switzerland on Jan. 22.
"Obviously the expectations have to be modest in this point of time," she said.
"MODEST SHIFT"
The United Nations estimates that 250,000 Syrians are living under siege as winter bites, most of them encircled by government forces, but also including 45,000 in two towns in the north that are besieged by anti-Assad rebels.
The UN Security Council issued a presidential statement on Oct. 2 calling for protection of civilians, demilitarisation of schools and hospitals, and improved access for aid workers.
"We are nowhere near that yet," Amos said. "We have seen a modest shift in terms of some of the administrative burdens ... (but) we are not seeing any progress in those areas so far."
Amos will convene a group of world powers and neighbouring countries - including Syria's allies Russia and Iran but not the Syrian government - for a second round of private meetings in Geneva this week, following similar talks on Nov. 26.
The head of MSF International, part of Medecins Sans Frontieres, also known as Doctors Without Borders, has written to the governments involved demanding an end to the Syrian government's control of aid, since it limits or bans assistance to opposition areas, especially medical supplies.
The United Nations began airlifting aid from Iraq on Sunday, as it was too dangerous to go by land, said Antonio Guterres, head of the UN refugee agency.
The UN is seeking $2.3 billion to help 9.3 million people in Syria next year, compared with its 2013 appeal of $1.4 billion, of which only 62 percent has been received.
For five neighbouring countries - Egypt, Iraq, Jordan, Lebanon and Turkey - it is seeking $4.2 billion to assist up to 4.1 million Syrian refugees and host communities who will be given food aid, including cash or vouchers.
"There is a tragedy in the plight of Syrian refugees, but let us not forget that they would have no place to go without the generosity of the neighbouring countries," Guterres said.
Guterres, a former prime minister of Portugal, urged European countries to share the burden and allow in Syrian refugees fleeing conflict or persecution.
"There is something fundamentally wrong when a Syrian family with women and children that has fled this dramatic conflict in Syria needs to take a boat with high risk of drowning to get to Europe," he said, describing Syria as "the most dangerous crisis for global peace and security since the Second World War".
The UN World Food Programme aims to feed 4.25 million people in Syria, where it reached only 3.4 million in November.
The overall UN appeal for 2014 also includes aid to Sudan, South Sudan, Yemen, Democratic Republic of Congo, Afghanistan and the Philippines.
