There was no immediate claim of responsibility for the attack. Picture used for illustrative purposes only.

An ambush on a bus in a remote eastern Syrian region left at least 15 pro-government fighters dead on Monday, the Syrian Observatory for Human Rights said.

The war monitoring group said it could not immediately confirm who carried out the attack, which took place in Raqqa province where the Daesh militant organisation is still active.

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Meanwhile, a ministry statement said that 11 government troops and two civilians were killed in what it said was a terrorist attack on a civilian transit bus. It said another three soldiers were wounded.

Syrian state news agency SANA said the attack took place in the Jabal Al Bishri region of the vast province of Raqqa.

The Syrian Observatory for Human Rights said the ambush had been carried out by Daesh sleeper cells that launch hit-and-run attacks in the country's desert areas.

There was no immediate claim of responsibility for the attack.

Syria's 11-year-old conflict has carved the country into various zones of control, with government troops and allied fighters controlling the most territory.

A patch of northwestern territory is held by Turkish-backed rebels and more hardline groups while Kurdish-led forces with US backing hold the northeast.

One of the deadliest bus ambushes was in December 2020, when 28 people were killed in an attack on a main highway in Syria's eastern Deir Al Zor province.