UN chief Ban Ki-moon says the use of food as a weapon against the Syrian people is a war crime amid reports of severe malnourishment in some besieged towns.

Some 400,000 people in Syria are under siege as a foreign-backed insurgency is wreaking havoc across much of the country.

"Let me be clear: the use of starvation as a weapon of war is a war crime," Ban said on Thursday. "I would say they are being held hostage, but it is even worse. Hostages get fed."

Ban's remarks came after humanitarian aid made its way into the town of Madaya in the southwest and Kefraya and al-Foua in Idlib Province which are besieged by militants.

The government recently agreed to facilitate the flow of relief aid into Madaya which is under the army siege.

Fifty trucks carrying international aid supplies left Damascus for Madaya on Thursday. Another convoy of 44 humanitarian aid trucks entered the city on Monday.

While the city has come under the spotlight amid claims of starvation, there has been a virtual media blackout on the situation in Kefraya and al-Foua.

Ban said, "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. This is utterly unconscionable."

Earlier, the Syrian government reiterated its commitment to cooperating fully with the UN and the Red Cross to deliver humanitarian aid to all civilians “without any discrimination.”

Last week, the Lebanese al-Manar TV said terrorist groups had hoarded aid packages for Madaya and sold it to the locals at inflated prices.

Syria’s Ambassador to the UN Bashar al-Ja’afari confirmed the report, saying aid delivered to Madaya had been looted by terrorist groups and sold to civilians.

By Press TV