The United Nations' food agency chief says the World Food Program is cutting back on assistance to thousands of Syrian refugees after an appeal for a ceasefire to help Syrians feed themselves went unheeded.

The WFP appealed in May for a humanitarian pause in fighting to let farmers harvest a bumper wheat crop in the country's northeast, an Islamic State movement stronghold, and bring it to markets in Syria's west.

WFP Executive Director Ertharin Cousin told The Associated Press on Friday that because there was no ceasefire, wheat is being stored at the farming belt and will likely be sold in Turkey.

She says WFP will halve the value of food vouchers for Syrian refugees in Lebanon and 440,000 Syrian refugees who live outside camps in Jordan will lose support.