A UN-brokered agreement that allows for the delivery of aid overland from Turkey into rebel-held areas of Syria expired on Monday after the Security Council failed to hold a vote to reauthorize it.

The 15 members of the council had been trying for days to find a compromise to extend the deal, which since 2014 has allowed for food, water and medicine to be trucked to northwestern Syria without the authorization of the government in Damascus.

But the vote, first scheduled for Friday, was postponed to Monday -- and then again to Tuesday morning, a source in the British mission to the UN, which holds the presidency of the Security Council, told AFP.

This means that as humanitarian convoys wrapped up their operations Monday night, the future of the aid corridor was in doubt -- it cannot resume operations until the United Nations reauthorizes it.

The aid mechanism originally allowed for four entry points into rebel-held Syria, though now only the Bab al-Hawa crossing remains passable. The accord comes up for renewal every six months due to pressure from Damascus ally Moscow.

The crossing provides for more than 80 percent of the needs of people living in rebel-controlled areas -- everything from diapers and blankets to chickpeas. The government in Damascus regularly denounces the aid deliveries as a violation of its sovereignty.

Negotiations continued all day at the UN Monday as officials scrambled to reach a last-minute deal but ultimately failed.

"We want to do all we can for the 4.1 million people in Syria who desperately need aid," British Ambassador and Security Council President Barbara Woodward said earlier in the day.

"We are still working very, very hard to find common ground with one and one goal only in mind: it's the humanitarian imperative, the needs on the ground," Swiss ambassador Pascale Baeriswyl said.

According to several diplomatic sources, the latest resolution -- drafted by Switzerland and Brazil -- would have allowed for a one-year renewal, as demanded by humanitarian workers.

But Russia, which in July 2022 vetoed a one-year extension, was again insisting it would only agree to another six-month deal, according to the same sources.

Switzerland and Brazil are now said to have put a nine-month renewal on the table.

UN humanitarian affairs chief Martin Griffiths had last week again called for the opening of more crossing points, for at least 12 months.

The situation "is intolerable for the people of the northwest, and those brave souls who help them to go through these ups and downs every six months," he said, pointing out that humanitarian agencies have to bring pre-positioned stock into the country every time access is threatened, in case the crossing is closed.

According to the UN, four million people in Syria depend on humanitarian assistance to survive following years of conflict, economic strife and devastating earthquakes.

After the earthquake in February, which killed tens of thousands of people in the country, Syrian President Bashar al-Assad agreed to the opening of two additional crossings, which remain open despite the Security Council's failure to reauthorize the Bab al-Hawa crossing Monday.

The authorization for the other two corridors is set to expire in mid-August.

"I have every hope that they will continue to be renewed. I see no reason why not," Griffiths said last week, after having met Assad in Damascus at the end of June.

Since the earthquake, more than 3,700 UN trucks carrying aid have passed through the three checkpoints. The majority have passed through Bab al-Hawa, including 79 Monday.