UNITED NATIONS: Instead of fleeing aerial bombings throughout winter, besieged Syrian children ran towards devastated buildings to search for broken furniture that could fuel fires for warmth and cooking, said a Syrian aid worker as the country marks five years of war.

The aid worker - who spoke on condition of anonymity because her group was operating without Syrian government approval - said despite the dangers of unexploded devices or further bombs the children still ran toward the sites of attacks.

"We've seen a lot of children ... running to collect the furniture," she said as aid group Save the Children launched a report on children under siege in Syria on Tuesday. "They wanted to use the wood in heating and cooking."

Save the Children said at least a quarter of a million children in Syria are living in besieged areas, where it said less than 1 percent of people had received United Nations food last year and only 3 percent received health assistance.

"There are regularly stories of children dying because they couldn't get the emergency aid and medical care that they needed," Sonia Khush, Save the Children's regional Syria director, told reporters.

According to the United Nations, some 486,700 people live in besieged areas - 274,200 people in areas besieged by the government, 200,000 in areas besieged by Islamic State and 12,500 people in areas besieged by opposition groups.

Save the Children and its partners spoke to 126 mothers, fathers and children in besieged areas and conducted 25 interviews with local aid groups, doctors, teachers and individuals for its 27-page report.

"Across the board the main thing that children said they fear is aerial bombardment," Khush said.

The report said children were forced to eat animal feed and leaves when food was sometimes just a few miles away in warehouses outside the besieged area and children had been forced underground to play and go to school.

"Children have really lost any sense of hope for the future," said Khush.

UN Syria mediator Staffan de Mistura said he hopes to reconvene peace talks in Geneva from Wednesday.

A cessation of hostilities agreement accepted by President Bashar al-Assad's government and most of his enemies, has reduced violence in Syria since it took effect on Feb. 27. The war has killed more than 250,000 people and caused the world's worst refugee crisis.