The World Food Program has suspended food aid to more than 1.7 million Syrian refugees in neighbouring countries, blaming a financing crisis caused by unhonoured cash pledges.
The Rome-based UN agency says refugees in Jordan, Lebanon, Turkey, Iraq and Egypt risk going hungry this winter if donors don't urgently provide the $US64 million ($A69.25 million) needed to finance the distribution of food vouchers through December.
"This couldn't come at a worse time," UN High Commissioner for Refugees Antonio Guterres said in a statement.
"I urgently appeal to the international community - support WFP now, don't let refugees go hungry."
While WFP didn't name which countries haven't made good on their commitments, foreign ministers from Germany, Finland and Sweden told reporters in Copenhagen their countries could do more to fill the funding gap.
"We have to strengthen our engagement and give humanitarian aid for the refugees and strengthen the structure of those countries who are hosting the refugees," German Foreign Minister Frank-Walter Steinmeier said.
WFP says refugees affected by the suspension of food aid include many children in Lebanon and Jordan facing harsh winters without adequate clothing or footwear, and living in tents already caked in mud that has made hygiene precarious.
Most in peril are the tens of thousands of families that are entirely dependant on international food aid, Guterres added.
Distribution of electronic food vouchers is to resume as soon as the pledged cash comes in.
WFP says it has fed millions of displaced people inside Syria and up to 1.8 million refugees in Lebanon, Jordan, Turkey, Iraq and Egypt in the three and a half years since the conflict erupted.
