The United Nations Secretary-General Ban Ki-moon reproached Syria's warring parties on Thursday, especially the Assad regime, for committing "atrocious acts" and "unconscionable abuses" against civilians in the country.
After briefing the UN General Assembly on his 2016 priorities, Ban Ki-moon told reporters the situation of the starving civilians in Madaya, which in his opinion showcases a new standard of low in war and shows "shocking depths of inhumanity."
"Let me be clear: the use of starvation as a weapon of war is a war crime," Ban said.
"I would say they are being held hostage, but it is even worse. Hostages get fed."
"All sides - including the Syrian government, which has the primary responsibility to protect Syrians - are committing atrocious acts prohibited under international humanitarian law," Ban stated.
The UN Security Council will be informed on Friday about 400,000 people who are under blockade in Syria, officials said. The meeting was demanded by Britain, France and the United States.
Ban indicated UN teams in Madaya had witnessed "scenes that haunt the soul."
"The 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," Ban said.
He also remarked that some 400 men, women and children in Madaya were in a horrific situation and were in desperate need of medical attention and that potential evacuation may be necessary.
Ban specified that some 400,000 civilians in Syria were besieged - about half in the country controlled by DAESH, nearly 180,000 in areas held by Assad regime and about 12,000 in Syria controlled by opposition groups.
"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 percent. This is utterly unconscionable," Ban stated.
He called key regional actors and world powers, especially the International Syria Support Group, to urge Syria's warring parties to allow for humanitarian aid to be delivered and to damp out indiscriminate weapons in civilian areas.
Meanwhile, UN spokesman Stephane Dujarric said on Wednesday that the Assad regime starvation tactics in Madaya could be considered a war crime as it imposed a blockade over cities to starve civilians to death.
On Monday, the first installment of humanitarian aid from the Red Crescent and the International Committee of the Red Cross reached Madaya, Foua and Kefraya in where thousands of civilians have been starving to death.
The Second convoy also left the Syrian capital Damascus on Thursday for the besieged Syrian town of Madaya and two rebel-held villages in the northwest, some 300 km (200 miles) from Madaya.
UNICEF confirms severe malnutrition in Madaya
The UN children's fund UNICEF on Friday confirmed cases of severe malnutrition among children in the besieged Syrian town of Madaya, where aid was delivered this week to thousands of people affected by the months-long blockade.
"UNICEF ... can confirm that cases of severe malnutrition were found among children," it said in a statement.
Dozens of deaths from starvation have been reported by monitoring groups, local doctors, and local aid agencies from Madaya, which is besieged by Syrian pro-government forces.
UNICEF said that out of 25 children under the age of five screened by its staff and the World Health Organisation, 22 showed signs of "moderate to severe" malnutrition.
Its staff also witnessed the death of a severely malnourished 16-year-old boy, it said.