UN Secretary-General Ban Ki-moon on Thursday called the deadly wave of starvation hitting areas of Syria under siege by government forces and other militant groups a "war crime."

"Let me be clear: the use of starvation as a weapon of war is a war crime," Ban said in a statement.

"All sides - including the Syrian government, which has the primary responsibility to protect Syrians - are committing this and other atrocious acts prohibited under international humanitarian law," Ban added.

Ban's statement comes after news that aid trucks reached the besieged Syrian town of Madaya, which gained notoriety in recent weeks following pleas from residents for food and other basic goods.

The International Committee of the Red Cross (ICRC) had held talks with the Syrian government, various armed groups and regional powers for nearly four months to gain permission to deliver aid to three besieged towns this week.

Six trucks, organized jointly by the ICRC, the Syrian Arab Red Crescent and the United Nations, brought flour, medicine, nutritional material, blankets, hygiene supplies and clothing into Madaya, according to Pawel Krzysiek, the ICRC's spokesman in Syria.

Madaya, which is located northwest of Damascus near the border with Lebanon, has been under siege for five months by fighters loyal to the Syrian government.

Also on Thursday, three trucks with aid supplies went into the villages of Foua and Kefraya in northern Syria. The villages have been besieged by rebels fighting to overthrow Syrian President Bashar al-Assad.

"There is possibly now a window of opportunity based on this positive development to make a significant step forward (...) in terms of lifting these sieges and stop with these medieval tactics of besieging towns and villages, and depriving people of humanitarian assistance," Dominik Stillhart, director of operations at the ICRC, said on Thursday.

Another convoy is expected to be sent to the town of Zabadani, close to the border with Lebanon, in the next few days, according to the UN.

Emergency UN Security Council meeting

France, Britain and the United States on Thursday requested an emergency UN Security Council meeting to demand the lifting of sieges in Syria and to allow aid deliveries to civilians facing starvation.

France's ambassador to the UN, Francois Delattre, said the meeting was due to be held on Friday. It "will draw the world's attention to the humanitarian tragedy that is unfolding in Madaya and other towns in Syria," he said.

UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein, speaking in Qatar, said those responsible for the sieges should be prosecuted.

"We condemn any such action," he said after a conference on human rights. "Starving citizens is a war crime under the international humanitarian law. Of course, any such action deserves to be condemned, whether it is Madaya or Idlib."

The commissioner continued: "Should there be prosecutions? Of course, that should be the case. At the very least there should be accountability for these crimes."

ls, jm/sms (Reuters, AFP, dpa)