Regional heads of U.N. agencies helping some 5.5 million Syrian refugees say they've received only 20 percent of $5.6 billion promised for 2018, warning that they'll soon have to scrap vital aid programs involving food, water and education.

Amin Awad of the U.N. refugee agency told a news conference Thursday that "this is an urgent and critical appeal" to international donors to disburse the money.

He says that without the funds, aid agencies "cannot be responsible for this number of refugees and this big numbers of host communities who have shown generosity during the last seven years."

Syria's civil war has displaced millions, including those who fled to neighboring countries such as Jordan and Lebanon, and those who were uprooted within Syria.

Refugee aid programs have faced chronic funding shortages.