The attack targeted a compound of Islamist armed opposition fighters in the town of Marea, some 30 kilometres north of Aleppo yesterday. The town, long a stronghold for Syrian rebels, has been near the front lines since the Islamic State group advanced into the area several months ago.
The Britain-based Syrian Observatory for Human Rights put the death toll in the bombing at seven people, including two rebel leaders. It said dozens were also wounded.
The discrepancy could not be immediately reconciled, but differences in casualty figures are common in the chaotic aftermath of attacks in Syria.
There was no immediate claim of responsibility, but suspicion fell on the Islamic State group, which frequently uses suicide attacks.
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Also yesterday, the Lebanese army said it killed three militants and wounded four others in a raid near the border with Syria.
The military said in a statement that it carried out the raid in the hills of Mkhairmeh based on information that "terrorist groups" were preparing logistics for combat operations there.
The Lebanese military occasionally clashes with Syria-based militants from the Islamic State group and the Nusra Front along the porous frontier.
Last year, militants from the two groups jointly raided the Lebanese border town of Arsal and captured about two dozen soldiers. Since then, they have killed four of the soldiers.