BEIRUT (AP) — At least 652 children were killed in Syria in 2016, making it the worst year yet for the country's rising generation, the United Nations' child relief agency said Monday.

There was no letup to attacks on schools, hospitals, playgrounds, parks and homes last year as the Syrian government, its opponents and the allies of both sides showed callous disregard for the laws of war.

UNICEF said at least 255 children were killed in or near schools last year and 1.7 million youngsters are out of school. One of every three schools in Syria is unusable, some because armed groups occupy them. An additional 2.3 million Syrian children are refugees elsewhere in the Middle East.

The figures come in a UNICEF report released two days before the sixth anniversary of the popular uprising that escalated into civil war.

Children were among the first victims of the government's brutal crackdown. On March 15, 2011, residents in the southern city of Daraa marched to demand the release of teenage students arrested for writing anti-government slogans on their school's walls. They were tortured in detention.

The report warns that coping mechanisms and medical care are eroding quickly in Syria, driving children into child labor, early marriage and combat. Dozens are dying from preventable diseases.

A report released a week ago by the international charity Save the Children said Syrian youngsters are showing signs of "toxic stress" that can lead to lifelong health problems, struggles with addiction and mental disorders lasting into adulthood.

The use of child soldiers is on the rise in Syria, UNICEF said. At least 851 children were recruited by armed factions last year, more than twice compared to the year before.

Children across the country are at risk of severe injury while playing around landmines and cluster munitions. Demining operations in opposition-held areas have been severely hampered by inaccessibility to outside experts.