The UN on Thursday said it was awaiting approval from the Syrian government before it can airlift humanitarian aid to besieged areas.
"You need the consent of the government," UN deputy Syria envoy Ramzy Ezzeldin Ramzy said at a Geneva press conference.
"I don't think there is something imminent," he cautioned.
However, late Thursday the Syrian mission to the United Nations said it had approved an aid delivery plan for the month of June to a number of areas.
Jan Egeland, a top UN adviser on humanitarian affairs for Syria, said airlifts would soon begin to al-Hassakeh in the far north, an area mostly under Kurdish control but with some government-held pockets.
Earlier Ramzy said that rebels and the government would have to comply to ensure staff safety during a "complex venture." Dropping supplies on urban areas would require helicopters, which could be exposed to attacks.
The International Syria Support Group (ISSG) - which includes the United States and Russia - last month pledged that if humanitarian aid was denied to besieged areas, the UN's World Food Programme (WFP) would be called on to carry out air drops starting June 1.
Britain, France and the US called Wednesday on WFP to plan on carrying out the air drops, losing patience with the slow pace of deliveries on the ground.
UN officials admit aid deliveries in May were far below expectations.
Much blame is placed on the Syrian government, including removing vital supplies from trucks and stopping aid deliveries from reaching rebel-held enclaves.
According to the UN, an estimated 492,000 people live in 19 areas under siege: 16 are held by rebels, while three are controlled by the government.
"Air delivery remains an option," Ramzy said, while stressing that the UN's preference is for land deliveries which are easier and cheaper.
The border from Iraq to the Kurdish areas of Syria has been closed of late, increasing the pressure on the local population. Turkey has also shut its border.
International medical charity Doctors Without Borders (MSF) said Turkey should open its borders to some 100,000 people fleeing fighting between rebel groups and Islamic State in northern Syria, while Europe should begin granting asylum to those escaping the frontlines.
"We ask Turkey to show this generosity once again and open its border to those trapped in Azaz," MSF said, also noting that Turkey already hosts 3 million refugees, mostly Syrians.
Meanwhile, a blast outside a mosque in Latakia city, a stronghold of President Bashar al-Assad, left three people dead and number of others injured, state media reported.
A woman was killed when rockets hit the outskirts of Qardaha, hometown of Syrian president Bashar al-Assad, the Britain-based Syrian Observatory for Human Rights said.
It added that dozens of shells fell on the regime-held areas of Aleppo in northern Syria, killing four people and wounding several others.
In Minbij, also in the north, a Kurdish offensive backed by the US continued for a second day against Islamic State.
The key Minbij pocket is the extremists' last territory on the Turkish border.
The operation is aimed at removing the militants from the Turkish border - 20 kilometres from Minbij - and supply routes, while also isolating Islamic State's de facto capital, al-Raqqa in north-eastern Syria.
Syrian rebels lost Minbij to Islamic State in 2014 after seizing it from al-Assad's forces in 2012.
Meanwhile, transport planes believed to be from the US-led coalition for the first time dropped weapons and ammunition over the city of Marea in northern Aleppo, the Observatory said.
Last week Islamic State fighters launched a surprise offensive on the Marea area and cut a vital supply line for the rebel groups inside the city.