Supplies made it into the starving Syrian town of Madaya this week, but for at least one teenager the aid came too late.
UNICEF workers who entered Madaya found severe malnutrition, overwhelmed health professionals "emotionally distressed and mentally drained" from working around the clock.
"UNICEF is particularly saddened and shocked to have witnessed the death of Ali, a severely malnourished 16-year-old boy who passed away in the town's clinic in front of our eyes," the organization said in a statement. "It is simply unacceptable that this is happening in the 21st century."
Madaya, a town of around 40,000 near Syria's border with Lebanon, has been besieged by pro-government forces for months. Horrific images of gaunt and emaciated locals sparked international outcry, prompting the Syrian government last week to agree on allowing aid into Madaya and two other towns — Kefraya and Foua — where residents were facing starvation.
What aid teams found there were "scenes that haunt the soul," according to United Nations Secretary General Ban Ki-moon.
"Elderly and children, men and women, who were little more than skin and bones: gaunt, severely malnourished, so weak they could barely walk, and utterly desperate for the slightest morsel," the U.N. chief told reporters on Thursday.
Both sides in Syria's long-running civil war have been accused of using starvation as a weapon — which constitutes a war crime.
Ban underscored that point when saying Thursday that the suffering in Madaya is "another low" in a conflict which already has reached "shocking depths of inhumanity."
"I would say they are being held hostage, but it is even worse. Hostages get fed," he told reporters on Thursday.
The U.N. Security Council will be briefed on Friday on the besiegement of some 400,000 people in Syria, according to Reuters.