An international children's group painted a grim picture of life in Syria's besieged cities, where young people have lost any hope for the future, living in constant fear of aerial bombardment and lacking access to food and proper medical care.

Save the Children said in a report published Tuesday that access to besieged areas by humanitarian organizations is virtually non-existent and only about 1 percent of food aid from the U.N. reached Syrians in besieged areas in 2015. About 250,000 children live in besieged areas, according to the report. "Children have really lost any sense of the future," Sonia Khush, the organization's regional director for Syria told a news conference at U.N. headquarters on Monday.

She described a life in which parents and their children are surrounded by warring groups and access to medicine or physicians is limited or non-existent. Children "barely know what fresh fruits and vegetables are" because the government or other combatants have blocked access to them, Khush said.

For the report, Save the Children, working with partners in Syria, interviewed 126 people in eight besieged areas, including children aged 10 to 16, parents and professionals such as doctors and teachers living in areas that have effectively become "open air prisons."

Syria's five-year war has killed at least a quarter million people and displaced half the country's population. The conflict, which erupted in March 2011 as a popular uprising against Syria's Bashar Assad's authoritarian rule, quickly descended into an all-out civil war that allowed militants such as DAESH to seize large swaths of land. Violence has eased in the country since the government and opposition agreed to a partial cease-fire 10 days ago.

According to diplomats, humanitarian aid has begun reaching some besieged areas thanks to a partial cease fire.

The resumption of talks has been expected ever since the U.S.-Russia-engineered truce, which has sharply reduced the bloodshed, took effect on Feb. 27. The cease fire though limited and tentative has mostly held, even as sporadic violence has continued.

An aid worker living in Syria who attended Monday's news conference but asked that her name not be used for fear of reprisals said food, medicine and other vital supplies are removed by combatants at checkpoints long before reaching the besieged areas. The situation is so precarious, she said, children routinely run to freshly bombed buildings to salvage wood from the wreckage to provide heat to stay warm, the aid worker said. Michael Klosson, vice president for policy and humanitarian response for Save the Children, said the only real way to get supplies to the people who need them is to end the siege of these areas and ensure sustained access. After five years of war, he said, "Enough is enough."