GENEVA — U.N. officials on Thursday all but rejected a call by a group of world powers for the United Nations to act unilaterally to air drop food to besieged Syrians, saying that Syrian President Bashar Assad has final say on any such deliveries.

Assad's forces have surrounded most of the 19 U.N.-designated “besieged areas” and there was no sign that his government would authorize air deliveries of aid.

The U.N. has dropped aid onto the city of Deir el-Zour, parts of which are loyal to Assad while other parts are controlled by Islamic State group fighters.

The International Syria Support Group, a coalition of world powers, had called for the World Food Programme to unilaterally deliver food to besieged Syrians starting Wednesday if access wasn't granted by the Syrian government.

Thursday's comments from Jan Egeland, a top humanitarian aid coordinator for Syria, and Ramzy Ramzy, deputy to U.N. Syria envoy Staffan de Mistura, suggested that the U.N. is unwilling to take that step.

Egeland said the companies who are subcontracted to carry out airlifts for WFP require government authorization. He said the government in Damascus hasn't provided permission for nearly all of the areas in need.

“The World Food Programme has not finalized its plans, I don't think there is something imminent, but I think the process that will lead to airdrops has already started,” Ramzy said in Geneva.

A day earlier, an aid convoy involving the U.N. and the International Committee for the Red Cross reached the town of Daraya, but it didn't include food aid. Egeland said he had “good hopes” the deliveries of food will happen “very soon.” He also said the U.N. was adding another town, al-Waer in Homs province, to its list of “besieged” areas — now numbering 19.

U.N. officials have repeatedly pointed to the high cost, complexity and security risk of air drops compared to delivering aid by road — which in addition usually allows for more aid to be delivered than is feasible by plane.

But access by road has been repeatedly rejected by the Assad government and its forces at checkpoints.

“At the end of the day, to be able to carry out these air deliveries — it's not just air drops, but air deliveries — you would need the consent of the government. I think that's quite clear,” Ramzy said.

The two U.N. officials said fighting near the northern city of Idlib is jeopardizing a vaccination campaign there.

Britain has called an emergency Security Council meeting due to take place Friday to discuss aid drops. Britain's U.N. Ambassador Matthew Rycroft said, “there has been some modest progress but that is too little too late.”