The UN World Food Programme warned today it was unable to help an estimated one million Syrians going hungry because of the civil war.
It said the Red Crescent was only able to get aid to 1.5 million of the 2.5 million people who are internally displaced in the country.
Spokeswoman Elisabeth Byrs said the dire security situation and inability to use the port of Tatous meant that many of the hardest-hit people would get no aid.
The torrid situation has already reached a flash point in neighbouring Jordan, where Syrian refugees furious over conditions in their camp attacked aid workers.
Seven were injured when dozens or refugees attacked them with sticks and stones while distributing breakfast.
Nearly 50,000 people at the Zaatari camp were battered by a winter storm, with many stranded by huge puddles and flooded tents.
Meanwhile Iran welcomed Syrian President Bashar Assad's Sunday speech outlining his view for peace.
Foreign Ministry spokesman Ramin Mehmanparast said the plan would improve the situation in Syria.
Most have not been so positive about the prospect for peace in Mr Assad's plan, which insisted he wouldn't talk to the rebels seeking to overthrow him.
UN secretary-general Ban Ki Moon said on Monday the plan "does not contribute to a solution that could end the terrible suffering of the Syrian people."
The UN estimates that more than four million people needed humanitarian assistance inside Syria in December 2012 and a million will need help outside Syria in the first half of 2013.
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