The United Nations food agency expressed alarm over images circulating on social media showing its food aid being distributed from boxes bearing the logo of the Islamic State group.
The World Food Programme said it was "extremely concerned" over the images, and that it was trying to verify the authenticity of the photographs and determine where they were taken.
"WFP condemns this manipulation of desperately needed food aid inside Syria," Muhannad Hadi, the agency's emergency coordinator for the Syrian crisis, said in a statement today.
"We urge all parties to the conflict to respect humanitarian principles and allow humanitarian workers including our partners to deliver food to the most vulnerable and hungry families," he added.
Images still circulating on Twitter today showed people, including children, gathered around and picking up boxes of food aid marked with the black and white flag of the IS jihadist group, which controls large swaths of territory in war-ravaged Syria and neighbouring Iraq.
In one photograph, a young man is shown carrying a box that appears to have the familiar light blue UN wreath logo barely hidden behind a shabby print of the IS flag.
It is not the first time the brutal group has been accused of seizing aid that enters its turf as part of its strategy of controlling the populations on territories it has taken.
WFP said the photographs seemed to have been taken in Dayr Hafr, in eastern rural Aleppo governorate, which it has been unable to reach with aid since last August 5.
At the time, its cross-line convoy delivered 1,700 food rations, or enough to feed 8,500 people for one month, it said.
"WFP has learned that in September 2014, ISIS raided Syrian Red Crescent (SARC) warehouses in Dayr Hafr where undistributed food rations may have been stored," the agency said, using an alternate acronym for the jihadist group.
"All areas controlled by ISIS are security hot spots, which severely limits the ability to monitor food distributions," it pointed out.
WFP has been operating in Syria since the country's bloody civil war erupted nearly four years ago.
It is currently delivering aid to more than four million people each month inside Syria and to 1.8 million refugees in neighbouring countries.
