The U.N.'s World Food Programme (WFP) is handing out rations to about 1.5 million people in Syria each month, still short of the 2.5 million deemed to be in need, WFP spokeswoman Elisabeth Byrs said.
Bread and fuel particularly are in short supply, but the WFP said it had won "special permission" from the government to import fuel from Lebanon to use in the trucks distributing aid in Syria.
The WFP is unable to increase assistance due to difficulty in reaching some insecure areas. Only a handful of aid agencies are authorised to distribute relief goods, some of which lack staff, fuel or other material.
"Our main partner, the (Syrian Arab) Red Crescent, is overstretched and has no more capacity to expand further," Byrs told a news briefing in Geneva.
More than 60,000 people have been killed during 21 months of conflict between the forces of President Bashar al-Assad and rebels trying to topple him.
Deteriorating security conditions forced the WFP to withdraw its staff from the towns of Homs, Aleppo, Tartous and Qamisly, Byrs said.
Long queues for bread are now normal in many parts of Syria and there are shortages of wheat flour in most parts of the country due to damage to mills, most of which are located in the embattled Aleppo area, she said.
Deliveries of food have been delayed by insecurity, and ships now have to use the Lebanese port of Beirut instead of the Syrian port of Tartous, Byrs said.
The United Nations last month appealed for $1.5 billion to help the millions of Syrians suffering from what it called a dramatically deteriorating humanitarian situation.
Four million people in the country need urgent humanitarian aid, including an estimated 2 million displaced from their homes by fighting.
The number of registered Syrian refugees has leapt from 500,000 to nearly 600,000 in the past month, U.N. figures show.
