Sixteen people, among them 10 children, were killed in a government air raid in east Syria on Wednesday, a monitor said, but state media blamed the deaths on jihadist militants.
The Syrian Observatory for Human Rights, a Britain-based monitor, said an air strike hit a bus on the road between eastern Deir Ezzor province and Damascus as it passed through the Shula area.
The group said most of the children were under the age of 10.
But state television said that the jihadist Islamic State group had killed the passengers, putting the death toll at 13 without specifying how they were killed.
It said most of those killed were women and children and said they were from the Shaitat tribe, which has engaged in clashes with the Islamic State in Deir Ezzor.
The Islamic State controls large parts of Deir Ezzor, including Shula, and has seen its strongholds in the province and elsewhere come under attack in stepped-up regime air raids in recent weeks.