Beirut (AFP) - Humanitarian aid drops to besieged areas in Syria are not imminent and need regime approval, the UN said Thursday, despite urgent calls from Britain and France for deliveries to start.
In northern Syria, meanwhile, a US-backed alliance of Kurds and Arabs pressed its advance towards the town of Manbij held by the Islamic State jihadist group.
And in the regime's coastal stronghold of Latakia, a suicide bombing near a mosque killed at least two people and wounded four others. Last month bombings claimed by IS in the nearby cities of Jableh and Tartus killed at least 170 people.
Humanitarian access in Syria has been a key sticking point in stalled UN-backed peace talks aimed at ending the five-year war that has killed at least 280,000 people and displaced millions.
Last month the United Nations said that if it did not see improvement on aid access to besieged areas by June 1, it would task the UN food agency to carry out air drops.
But a deputy to the UN special envoy to Syria Staffan de Mistura said on Thursday: "As long as the World Food Programme has not yet finalised its plans, I don't think there's something imminent."
Ramzi Ezzedine Ramzi stressed air drops were "a very complex venture" which would need approval from Damascus.
De Mistura pointed out last week that it can take six weeks of air drops to deliver the same amount of aid as a single convoy over land.
- 'Too little, too late'-
On Wednesday land deliveries reached two towns besieged by government forces where civilians are facing food shortages.
A truce allowed a convoy to enter the town of Daraya near Damascus for the first time since late 2012, while another entered the nearby town of Moadamiyeh for the first time since March.
But Syria's opposition said only medical supplies were in the Daraya delivery and British charity Save the Children said it was "shocking and completely unacceptable" that it excluded desperately needed food.
An estimated 8,000 people live in Daraya, one of the first towns in Syria to erupt in anti-government demonstrations in 2012 and one of the first under a strict regime siege the same year.
"Daraya needs everything" including food, medicine and fuel, said an activist inside the town.
"Some items come in through smuggling because some people risk their lives to slip out of town," said Shadi Matar.
"For a long time we relied on medicine past its sell-by date. But we didn't have even that for most types of medicine."
The United Nations says a total of 592,000 people live under siege in Syria -- most surrounded by government forces -- and another four million in hard-to-reach areas.
Britain has called for an emergency UN Security Council meeting on Friday to discuss humanitarian access and to press ahead with air drops.
"It's too little, too late," said Matthew Rycroft, the British ambassador to the UN, referring to Wednesday's deliveries.
- Anti-IS offensive -
French ambassador Francois Delattre, who holds the council presidency this month, called for air drops to all areas in need and blamed the Syrian regime for blocking access to villages and towns under siege.
Staunch regime ally Russia on Wednesday said that the local truce in Daraya would be observed until 00:01 am on Friday (2101 GMT Thursday) to allow aid deliveries.
But Russia's ambassador Vitaly Churkin suggested plans to air drop humanitarian relief could be put on hold.
"I think we need to continue to pursue with land deliveries," he said.
In north Syria, fighters from the Kurdish-Arab alliance were 10 kilometres (six miles) outside the IS-held town of Manbij, a monitor said.
The Syrian Democratic Forces alliance had seized some 20 villages outside the town, said the Syrian Observatory for Human Rights.
The US-backed SDF last week launched an offensive north of the jihadists' Syrian stronghold of Raqa city.
This week the alliance opened a new front towards Manbij, which lies on a key supply route between the IS-held town of Jarabulus on the Turkish border and Raqa.
Syria's main opposition group on Wednesday called on the UN to implement a truce in all of the country except areas under IS control during the holy month of Ramadan which begins next week.
In Syria's second city of Aleppo, at least five people were killed in regime rocket fire on a rebel-held district, the civil defence said.