Sixteen people, among them 10 children, were killed in a government air raid in eastern 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 the province of Deir Ezzor and Damascus as it passed through the Shula area.
It said most of the children were under the age of 10.
But state television said 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.
The Observatory said another government air strike in the east of the province on Wednesday afternoon destroyed a building being used as a headquarters and a prison by Islamic State militants.
The strike in the village of Ghareebeh killed at least five IS militants, and allowed some of the people being held in the prison to escape, the Observatory said.
In Damascus province, the toll in regime shelling on the city of Douma rose to at least seven, among them a child, the monitor said.