Regime airstrikes and artillery fire in northwestern Syria, including on schools in the city of Idlib, killed 19 civilians on Tuesday, said the Syrian Observatory for Human Rights.
The war monitor said eight children were among those killed in the raids on Idlib city and the towns of Binnish and Maarat Misrin.
It said schools were hit in Idlib, the main city in the densely populated, ever-shrinking enclave of the same name -- the last major territory in Syria still controlled by opposition and extremist factions.
At least six children were among 10 civilians killed in Maarat Misrin, a town just north of Idlib city on the road to the Turkish border, the Observatory said.
"Among the six killed in Idlib were one schoolchild and three teachers," said Rami Abdel Rahman, the head of the UK-based monitoring group.
Another three people, one of them a child, were killed in strikes on Binnish, northeast of Idlib city.
Save The Children called for schools to be spared.
"Schools must be safe havens for children, even in a conflict zone," the charity's Syria response director Sonia Khush said.
"Today's attacks are another sign that fighting in North West Syria has reached catastrophic levels of violence against children and civilians."
'Not even school'
According to the Observatory, pro-regime forces retook control of 15 villages and towns in the southern part of the Idlib enclave.
With backing from Russia, Damascus and allied forces have in recent weeks pressed a major offensive against the last bastion of opposition to the regime.
The territory still held by extremists and Turkish-backed factions has shrunk to an area roughly the size of Majorca, hosting more than three million people -- half of them already displaced by violence elsewhere.
The offensive has displaced close to a million people since December, amid bitter winter cold.
Syrian and Russian raids have repeatedly targeted schools and health facilities in the area, despite appeals from aid groups and world powers to respect international law.
Several countries and the United Nations have called for an urgent ceasefire in Idlib, where the current humanitarian emergency has been described as the worst since the start of the Syrian conflict nine years ago.
"Vast numbers of families have been forced from their homes many times in search of some semblance of safety and stability," Khush said.
"Still they face daily and nightly terror as bombs rain down. Nowhere is safe, not even school."
Russia earlier this month blocked a UN bid to end the Damascus regime's assault on Idlib.
Many of the crowded territory's residents are civilians who were forced from their homes in earlier phases of a war that has displaced more than 11 million people since 2011.
According to the UN's Office for the Coordination of Humanitarian Affairs, some 170,000 people are sleeping rough in Idlib province, which saw snow and sub-zero temperatures earlier this month.
