“Any money going to Assad and his allies shows that the UN is not impartial but is in fact helping the largest player in the conflict,’’ said Kathleen Fallon, a spokeswoman for The Syria Campaign, an independent advocacy group.

“The regime has been responsible for the majority of the deaths, and they are being rewarded. It sends the wrong message.’’

The group accused the UN of losing all impartiality in the six-year civil war in an investigation published last year. After interviewing dozens of current and former UN staff, researchers accused the body of allowing Assad a veto over the delivery of humanitarian supplies, thereby “enabling” the regime’s use of “sieges as a weapon of war”. Almost one million people are living in 52 blockaded areas of Syria, of which 49 are under siege by Assad’s forces.

They said the UN was failing the most desperate by acquiescing in the regime’s policy of denying food and medicine to the 49 rebel-held areas.

Last year, almost 90 per cent of UN requests for aid deliveries were either ignored or denied by the regime.

One UN official said that these were already “censored at the agency level”, meaning that the number of requests was kept low so as not to “annoy” the authorities.