With violence escalating in Aleppo and elsewhere across war-ravaged Syria, the United Nations said Saturday that the number of children trapped in besieged areas had doubled in less than a year to half a million.

A report by Unicef, the United Nations Children’s Fund, said the children were among hundreds of thousands of civilians in 16 areas under siege across the country who had been “almost completely cut off from sustained humanitarian aid and basic services.”

The report said some of these areas had received little or no aid in nearly two years, despite repeated efforts by international relief agencies to provide food and medicine. “This is no way to live,” Unicef’s executive director, Anthony Lake, said in the report.

The report estimated that 100,000 of the trapped children were among the civilians pinned down in eastern Aleppo, the insurgent-held portion of what had been prewar Syria’s commercial epicenter.