UN officials and volunteers from the Syrian Arab Red Crescent are vaccinating children and distributing desperately needed aid for the first time in a remote camp for the displaced on Syria's border with Jordan
Residents said international organizations entered Rukban Camp for the first time since it was set up more than three years ago and where nearly 50,000 people have been stranded.
Before January, aid only reached the camp from Jordan and aid workers were barred from accessing the camp for security concerns.
A UN spokesperson said Secretary General António Guterres welcomes the delivery of humanitarian aid to Rukban, and is calling for continued, full, safe, sustained and unimpeded humanitarian access to ... and to all people in need throughout the country.
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Fadwa Baroud of the UN Office of the Resident Coordinator said it was the first time a UN aid convoy had accessed Rukban camp from inside Syria.
Before January, aid only reached the camp from Jordan and aid workers were barred from accessing the camp out of security concerns.
A convoy of 78 trucks reached the camp late Saturday and residents posed with the aid trucks driving through the desolate camp, where 10,000 children are expected to be vaccinated.
The US-led coalition fighting against Islamic State militants said its local allies, a Syrian armed group known as Maghawir al-Thawra, provided security for the aid convoys.
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Russia, a close ally of the Syrian government, blames the United States for the deterioration of the situation in Rukban, which is within a 55-square kilometer "deconfliction zone" set up by US forces.
The US-led coalition has denied such allegations and blamed Russia and the Syrian government instead.
"We continue to stand ready to enable future delivery of UN humanitarian relief to the people of Rukban until they are able to return home as we pursue our mission of an enduring defeat of [IS],'' said Maj. Gen. (UK) Christopher Ghika, a deputy commander for the US-led Coalition.
The UN said aid deliveries would continue for up to four days, describing the condition in the camp as "critical" with reported shortages of basic commodities, protection concerns, and increasing violence.