UN agencies have launched what they say is the biggest-ever relief appeal for a single emergency, as they called for $US6.5 billion ($A7.3 billion) in funds for Syrians in 2014.
The UN's humanitarian affairs and refugee agencies said on Monday that $US2.3 billion is needed to provide for people inside the war-torn country, with the remainder for Syrian refugees in the region.
"We're facing a terrifying situation here, where, by the end of 2014, substantially more of the population of Syria could be displaced or in need of humanitarian help than not," UN High Commissioner for Refugees Antonio Guterres said in Geneva.
"This goes beyond anything we have seen in many, many years, and makes the need for a political solution all the greater."
The agencies warned that they were planning for up to 4.1 million refugees by the end of 2014 - of a total pre-war population of 22.4 million.
More than 2.3 million Syrians have so far fled the country since the conflict began in 2011, with more than 4 million estimated to be displaced inside its borders.
The UN's World Food Programme (WFP), one of the bodies participating in the multi-agency plan, separately announced it would feed 4.25 million Syrians next year, at a cost of $US2 billion.
The WFP said almost 6.3 million people in the country needed "urgent, life-saving, food assistance".
It pledged to focus on preventing child malnutrition, giving food supplements to 240,000 children aged 6 to 23 months.
Meanwhile, Italian diplomatic sources quoted by local media said Norwegian and Danish ships due to transport chemical weapons out of Syria would stop at an undisclosed Italian port, where their cargo would then be transferred onto a US Navy vessel.
Syria's chemical arsenal is being dismantled under the supervision of the Organisation for the Prohibition of Chemical Weapons.
The country agreed to dispose of its weapons in line with a Russia-US deal, amid international outrage after hundreds died in a chemical weapons attacks in rebel-held areas outside Damascus in August.
An opposition watchdog raised its estimated death toll from Syrian government air raids in the northern city of Aleppo on Sunday to 76.
Those killed in the raids, in which explosive-filled barrels were dropped from helicopters over rebel-held areas, included 28 children, the Britain-based Syrian Observatory for Human Rights said.
The Syrian uprising started in March 2011 with anti-government protests, but descended into civil war after President Bashar al-Assad's regime sought to quell the demonstrations with violence.
More than 100,000 people have been killed, according to UN estimates.
