Aid convoys reached the besieged towns of Madaya, Foua and Kefraya on Monday. Since then, aid workers have reported horrifying scenes of malnutrition and deprivation.
Meanwhile, U.N. officials are emphasizing that the need in Syria extends far beyond those towns. Almost 400,000 people are living in besieged areas in Syria, the U.N. says.
Dr. Rajia Sharhan, a nutritionist with UNICEF, was on one of the convoys arriving in Madaya this week. She described what she found to NPR's Rachel Martin on Weekend Edition Sunday.
"We saw children, we saw adults, mothers all suffering from malnutrition ... their bodies were too weak even to move around or to talk," she said.
In the basement of a makeshift hospital, she came across two children lying on a bed. "Both of them had severe, acute malnutrition complications — one of them was dying in front of our eyes," she says. She tried to resuscitate him, but couldn't save his life.
When she turned to the boy next to him, who was so weak she could barely find his pulse, he was pleading with her, asking what had happened to the other child. She tried to calm him down.
" 'Did he die? Did he die?' " Dr. Sharhan remembers him asking.
The second boy survived, and was evacuated out of Madaya.
Many weren't so lucky — Doctors Without Borders says a total of 35 people have died of starvation in Madaya, including seven who died as aid convoys were being prepared, and five who died after the convoys arrived.
Dr. Sharhan noted that thousands of Syrians across the country, not just in Madaya, are facing starvation.
"Syria is under war. And war makes everything difficult," she says. "But we are advocating strongly and asking all sides to lift the siege on all the communities in Syria and provide unimpeded, unconditional humanitarian access."
It's a call that's echoed at the highest levels of the U.N. Speaking to the press on Thursday, Secretary-General Ban Ki-Moon said that U.N. teams providing aid "have witnessed scenes that haunt the soul."
"I want to make a special plea for those in besieged areas of Syria," he said. "I would say they are being held hostage — but it is even worse. Hostages get fed."
He said of the almost 400,000 people besieged in Syria, about half are under siege by ISIS, about 180,000 by the Syrian government and its allies, and about 12,000 by armed Syrian rebels.
"In 2014, the UN and partners were able to deliver food to about 5 per cent of people in besieged areas. Today, we are reaching less than 1 per cent," Ban said.
"This is utterly unconscionable."
On Monday, Abeer Etefa of the UN's World Food Program told NPR's Kelly McEvers that besieged areas have been cut off for months — and some areas have never been reached by aid convoys.
And it's not enough for a town to receive a single delivery of aid, she says.
"We need regular, unimpeded access," she said. "We cannot send food that's enough for a year and let people [be] besieged. We have to reach them on monthly basis."
Ban called the use of starvation as a weapon a war crime, and called on the U.N. Security Council to find a solution to the crisis in Syria.
Syrian peace talks are set to resume in Geneva on January 25.