"This conduct amounts to the stealing of food from the mouths of hungry people," WFP Executive Director David Beasley was quoted by Reuters as saying. "At a time when children are dying in Yemen because they haven’t enough food to eat, that is an outrage. This criminal behaviour must stop immediately."

The WFP said its monitors have gathered evidence, including images, of food being illicitly removed from aid distribution centres, as well as proof that local officials are falsifying records and manipulating the selection of beneficiaries.

"It was discovered that some food relief is being given to people not entitled to it and some is being sold for gain in the markets of the capital," the WFP statement said.

The UN body has contacted the Houthis and urged that food aid reach those in need.

The Yemen conflict has triggered what the UN calls the world's worst humanitarian crisis, with 14 million Yemenis now at the brink of mass starvation.

WFP spokesman Herve Verhooselhas said that the UN body is considering the possibility of distributing cash to those in need of aid with the use of a biometric identification system.