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.
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"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.