An attack in eastern Syria killed 10 oil field workers, state news agency SANA reported on Friday, a day after Syrian Kurdish-led forces announced an offensive against jihadists.
In addition to the nearly dozen dead, "two others have been wounded in a terrorist attack that targeted three buses transporting workers from al-Taim oil field in Deir Ezzor" province, SANA reported.
It did not provide any information on the nature of the attack in the Kurdish-held area or who may be behind it, but a British-based war monitor said "cells of the Islamic State group" carried out the assault near the oil field.
"The attack began with explosive devices that went off as the buses drove by, and then the group's militants shot at them," Rami Abdel Rahman, director of the Syrian Observatory for Human Rights, told AFP.
On Thursday the Kurdish-led Syrian Democratic Forces said they had begun an offensive against Islamic State (IS) group fighters, following an earlier jihadist assault on a prison in Raqa, northwest of the attack on the bus.
The Syrian Democratic Forces (SDF) said the offensive, dubbed "Operation al-Jazeera Thunderbolt", aimed to "eliminate" IS fighters from areas that had been "the source of the recent terrorist attacks."
The SDF said it was carrying out the operation alongside the U.S.-backed coalition, although there was no immediate confirmation from the international force that they were taking part.