Syria's authorisation of some aid convoys to besieged towns is "at best a drop in the ocean" and the UN must urgently prepare to make air drops to areas most in need of humanitarian help, France's UN ambassador said.
The Syrian government announced a day earlier that it approved the delivery of aid to 36 "restive areas" and partial deliveries to eight other areas in June. The five-year-old civil war in Syria has killed some 250,000 people.
"We have not been fooled by the Syrian regime's ploy to authorise certain convoys which turn out to be empty of food or medicine or both," Francois Delattre told reporters ahead of an emergency closed-door meeting of the UN Security Council to hear briefings from the UN special envoy for Syria and the UN humanitarian chief.
Britain's UN ambassador Matthew Rycroft said "it's too little, too late, but it's welcome".
The United Nations had requested access to 34 locations to help 1.1 million people and Syria approved 23 requests in full and six partially, and rejected five, UN humanitarian spokeswoman Amanda Pitt said.
The request included all 19 locations officially designated as besieged areas, except Yarmouk, which is covered by the UN agency for Palestinian refugees and Deir el-Zour, which is under siege by Islamic State extremists and is already receiving air drops, she said.
Of the 17 besieged locations that the UN sought to send aid, Ms Pitt said Syria approved 12 requests in full and three partially - Moadamiyeh, Daraya and Douna, where it approved medical assistance, school supplies and milk for children.
Syria rejected UN requests to send aid to Zabadani, a mountain resort which has been besieged by government forces and Lebanon's Hezbollah fighters since last year, and Waer, the last rebel-held neighbourhood in the central city of Homs, Ms Pitt said.
The International Syria Support Group, a coalition of world powers, had called for the World Food Programme (WFP) to unilaterally deliver food to besieged Syrians starting June 1 if access was not granted by the Syrian government.
WFP said UN officials are appealing to the Syrian government to get permission for air drops to besieged areas.
The UN food agency said it is "activating" the air delivery plan following a request from the Syria support group, led by the US and Russia, but that it needs authorisations and funding first.
WFP said late on Thursday that 15 besieged areas would require helicopter operations for the air drops if land access is not granted.
It said high-altitude air drops would be possible in the villages of Fouah and Kfraya, in addition to the north-eastern city of Deir el-Zour where air drops have already taken place.