The United Nations says one million Syrians are hungry and helpless due to the civil war.
The World Food Programme is helping 1.5 million Syrians, but the BBC reports that continued fighting and the agency's inability to use the port of Tartus mean many people are not receiving aid.
The UN estimates that more than 60,000 people have been killed in the uprising which began in March 2011.
Rebels have gained control of swathes of northern Syria in recent months.
WFP personnel have been pulled from offices in Homs, Aleppo, Tartus and Qamisly due to an increasingly dangerous situation.
Meanwhile, the UN refugee agency said the number of refugees fleeing the violence in Syria rose by nearly 100,000 in the past month.
It said there were 597,240 registered refugees and individuals awaiting registration as of 6 January - up from 509,559 the month before.