Ertharin Cousin, the UN agency's executive director, called on donor countries to give more to millions displaced by the Syria conflict, now in its fifth year.
"We need everyone to recognise that we as a global community must continue to stand by these families, these children, until the political situation is solved," she told The Associated Press after meeting with refugees in the Jordanian capital, Amman.
Since the start of the Syrian conflict in 2011, more than 4 million Syrians have fled to neighbouring countries. About 630,000 have found refuge in Jordan, with the vast majority living in poverty in local communities rather than in three refugee camps. Other host countries include Lebanon, Turkey, Iraq and Egypt.
In Jordan, some 440,000 refugees currently receive WFP food vouchers, with aid scaled back repeatedly in recent months.
The rest are considered less vulnerable because family members could potentially find informal jobs, even though refugees are largely barred from working in Jordan.
"Unfortunately, those families, starting in September, unless we receive additional contributions, they will receive nothing," Cousin said.
In Iraq, meanwhile, the WFP announced further cuts in food aid for close to one million displaced people.
"The situation is bleak," Cousin said after meeting Khaldiyeh Hussein, a mother of eight, in her one-room shelter in the Hashemi al-Shamali neighbourhood of Amman.
