Islamic State said on Monday they were responsible for a suicide bombing on a bus on Sunday which killed fighters from western-backed Syrian rebel groups near the Atmeh border crossing with Turkey.
In a statement on one of its Telegram channels, the hard-line militant group said it killed 50 rebels traveling on the bus, from the Failaq al-sham and the al-Zinki groups.
It said the rebels were traveling to fight against Islamic State in northern Aleppo province.