A convoy carrying urgently-needed aid for 50,000 civilians stranded on the Syria-Jordan border has been postponed for security reasons, the UN says.
Forty-five lorries were due to arrive on Saturday at the Rukban camp, which last received aid in January.
Syria's army controls access to Rukban, which is near a US-backed rebel base. Jordan is also blocking aid deliveries.
There have been reports of children dying due to poor sanitary conditions and a lack of healthcare at the camp.
"The dire humanitarian situation cannot be allowed to continue," UN Emergency Relief Co-ordinator Mark Lowcock told the Security Council.
"The UN is ready and willing to proceed with the convoy immediately."
Allow Twitter content?
The Rukban camp has been called "one of the most desperate places in Syria".
It a cluster of about 10,800 makeshift tents and mud huts in the country's remote eastern desert, just north of a raised sand barrier, or berm, where the Syrian, Jordanian and Iraqi borders converge.
The camp is also inside a 55 sq km (20 sq mile) "deconfliction zone" set up around the at the nearby Tanf military base by US forces supporting rebel fighters battling the jihadist group Islamic State.
The UN estimates that 80% of the people stranded at Rukban are women and children. They began arriving in the area in late 2015 after fleeing areas of Syria previously controlled by the militant group IS.
They wanted to cross into Jordan, which has taken in 670,000 Syrian refugees since the civil war began in 2011, but the kingdom sealed the crossing near Rukban in June 2016 after six soldiers were killed in a bomb attack claimed by IS.
Jordan insisted the camp had to be supplied from Syria, but did allow occasional aid deliveries until January. Since then, residents have had to rely on what the UN has called a "trickle" of commercial deliveries.
But even those dried up last month, when Syrian government forces reportedly blocked roads to the camp after the failure of a reconciliation deal with rebel groups in the area. Prices for food and basic supplies increased significantly.
"It is barbaric and illegal under international law to deny these civilians aid. Children are facing horrific malnutrition and are drinking contaminated water," said Dr Hussam Al Fakir of the charity Union of Medical Care and Relief Organizations (UOSSM) on 15 October.
"Pregnant women are giving birth in the desert without even the most basic medical care. Those that desperately need caesarean sections have not been allowed to leave the camp and are in a perilous situation."
Allow Twitter content?
At least a dozen deaths have been reported since then, according to Reuters news agency, and the UN Children's Fund (Unicef) has also confirmed that two children - a five-day-old boy and a four-month-old girl - died on 8 October because they could not access a hospital.
A UN-supported clinic on the Jordanian side of the border is providing basic health services for urgent life-saving cases, but more sophisticated healthcare is required that is only available in hospitals.
The UN has said it has received authorisation from the Syrian government to deliver aid to Rukban, and that there is an ongoing discussion to "identify means to deliver the humanitarian assistance, while ensuring the safety of the humanitarian workers". But it has not given a date.
Unicef has warned that the situation will worsen further with the cold winter months approaching, especially when temperatures dip below freezing point.