AMMAN (Reuters) - United Nations-led aid delivery, critically needed by thousands of civilians stranded in a camp on the Syrian-Jordanian border, has been postponed and will not arrive on Saturday as was expected by community leaders, a U.N. official said on Friday.

“The planned joint U.N.-Syrian Arab Red Crescent (SARC) humanitarian convoy to Rukban camp has been delayed for logistical and security reasons,” Fadwa Abed Rabou Baroud, a Damascus-based U.N. official, told Reuters.

“The U.N. remains ready to deliver aid for the 50,000 people in need as soon as conditions allow,” Baroud added.

In the last three years, tens of thousands of people have fled to the camp from Islamic State-held parts of Syria being targeted by Russian and U.S.-led coalition air strikes.

A siege earlier this month by the Syrian army and a block on aid by Jordan has depleted food at the desert camp where the borders of Syria, Jordan and Iraq meet.

That has led to at least a dozen deaths in the past two weeks among its more than 50,000 inhabitants, mainly women and children, residents and U.N. sources told Reuters.

Community leaders said heavy sandstorms had hit the makeshift camp in the last forty eight hours.

“The U.N. have coordinated very well with us but the delay could well be due to the weather conditions and the sandstorms, anyway the reason for the delay will become clearer in the next day or two,” Oqba al Abdullah, an official inside the camp said.

Rukban lies inside a “deconfliction zone” set up by U.S. forces. Damascus says U.S. troops are occupying Syrian territory and providing a safe haven for rebels.

The United Nations office said it had received authorization by the Syrian government to deliver the aid and confirmed preparations were being made for a convoy to desperate camp residents this week but did not give a date.

U.N. officials had been pressing Moscow for months to get its ally Damascus, which had said the camp harbored terrorists, to agree to aid reaching residents to stave off starvation.

The “deconfliction zone” is designed to shield U.S. troops at the Tanf garrison and maintain for Washington a strategic foothold in an area close to a crucial supply route for Iranian weapons entering Syria from Iraq.

Western diplomats believe the siege of the camp was part of a Russian-led effort to put pressure on Washington to get out of Tanf.

U.S. Marines conducted rare military exercises in the base last month and General Joseph Votel, head of U.S. Central Command, made an unannounced visit to Tanf this week.