At least four Syrian school children were killed and 10 wounded on Monday when a regime air strike hit their bus in the northwest of the country, a monitor said.
The Syrian Observatory for Human Rights said most of those wounded and killed when the Syrian air force hit a school bus near the village of Jubass in Idlib province were under the age of 10.
"The toll could go rise as there are serious injuries," said the monitor, which has a wide network of sources on the ground across Syria.
Idlib is largely in the hands of Syria's Al-Qaeda franchise, Al-Nusra Front, which in recent weeks has fended off advances by rival rebel groups and now holds two strategic military bases in the province.
Syria's air force is a significant tool in the arsenal of President Bashar al-Assad, whose forces have fought a devastating conflict against insurgents since 2011.