Two convoys of aid supplies were delivered this week to the town of 42,000 affected by the months-long blockade. The U.N. said a convoy was planned to Madaya, which is besieged by pro-government forces, and two rebel-besieged villages of Foua and Kefraya in Idlib next week and that regular access was needed.

"UNICEF ... can confirm that cases of severe malnutrition were found among children," it said in a statement, after the United Nations and Red Cross had entered the town on Monday and Thursday to deliver aid for the first time since October.

UNICEF spokesman Christophe Boulierac told a news briefing in Geneva UNICEF and World Health Organization staff were able to screen 25 children under five for malnutrition and 22 showed signs of moderate to severe malnutrition. All were now receiving treatment. A further 10 children aged from 6 to 18 were screened and six showed signs of severe malnutrition, he said.

UNICEF staff also witnessed the death of a severely malnourished 16-year-old boy in Madaya, while a 17-year-old boy in "life-threatening condition" and a pregnant women with obstructed labor needed evacuation, Boulierac said.

World Food Program (WFP) spokeswoman Bettina Luescher said that the local relief committee in Madaya had provided figures on the extent of starvation, but it could not verify them.

"Our nutritionist...was saying that it is clear that the nutritional situation is very bad, the adults look very emaciated. According to a member of the relief committee 32 people have died of starvation in the last 30-day period."

Dozens of deaths from starvation have been reported by monitoring groups, local doctors, and aid agencies from Madaya.

U.N. Secretary-General Ban Ki-moon said on Thursday Syria's warring parties, particularly the government, were committing "atrocious acts" and condemned the use of starvation as a weapon of war in the nearly five-year-old conflict.

"It can also be a crime against humanity. But it would very much depend on the circumstances, and the threshold of proof is often much more difficult for a crime against humanity (than for a war crime)," U.N. human rights spokesman Rupert Colville told the briefing on Friday.

The United Nations says there are some 450,000 people trapped in around 15 siege locations across Syria, including in areas controlled by the government, Islamic State and other insurgent groups.

"Let us not forget that in addition to Madaya, across Syria there are 14 other Madayas and these are locations where different parties to the conflict have been using siege as a tactic of war, depriving children and innocent civilians from accessing life-saving supplies and services," Boulierac said.

Reuters