Nearly 2 million Syrian refugees are facing a food crisis after a lack of funds prompted the UN's World Food Programme (WFP) to stop delivering aid.
Syrian refugees in Lebanon, Egypt, Turkey, Jordan and Iraq were receiving WFP food vouchers, but the programme was stopped due to a shortfall of $64m (£40m).
"A suspension of WFP food assistance will endanger the health and safety of these refugees and will potentially cause further tensions, instability and insecurity in the neighbouring host countries," said WFP executive director Ertharin Cousin in an appeal to donors, adding that commitments by many countries have remained unfulfilled.
"The suspension of WFP food assistance will be disastrous for many already suffering families."
The WFP also added that many refugees are living in appalling conditions and are not prepared to face another harsh winter. If new funding arrives in December, WFP will immediately resume assistance for refugees who use electronic vouchers to buy food in local shops.
"Since the start of this operation, WFP's voucher programme has injected about US$800m into the economies of refugee hosting countries which border Syria", it said.
The appeal by the WFP came a few months after the UN urged donor countries to pledge more money to help displaced Syrians, victims of a more than three-year conflict, saying that the money pledged until that moment represented only half of the funds needed to support people.
The UN's appeal followed Amnesty's warning of the risk of mass starvation in Syria.
Philip Luther, director of Amnesty International's Middle East and North Africa Programme, previously said: "The world's response to the Syria crisis has been woefully inadequate. At the end of 2013 the UN humanitarian appeal - the largest in the organisation's history - was just 70%-funded."
The Syrian civil has pitted President Bashar al-Assad supporters against rebels, causing the deaths of hundreds of thousands of civilians.
According to latest estimates, at least 191,000 people have been killed in the conflict while millions have fled their homes.