A senior commander in Syria's powerful Islamist Ahrar al-Sham rebel group was killed Saturday night in a suicide bombing in Idlib province, a monitoring group said.
"Ahrar al-Sham chief of staff Majed Hussein Al Sadeq was killed with three other fighters from the group in a suicide attack against its headquarters in Binnish town," northeast of Idlib city, the Syrian Observatory for Human Rights said.
"An unknown person parked his motorcycle near the headquarters then walked into a group of Ahrar al-Sham fighters and detonated his explosive belt," the observatory said.
It was unclear who was responsible for the attack.
Sadeq, also known as Islam Abou Hussein, was a Syrian army officer who defected to join the opposition. He held several posts in Ahrar al-Sham before becoming its chief of staff.
Ahrar al-Sham is one of Syria's most powerful rebel groups, founded in 2011 and financed by Turkey and Gulf states, according to experts.
It is a leading member of the Army of Conquest alliance that controls the northwest province of Idlib along with Al-Qaeda affiliate Al-Nusra Front.
AFP contributed to this report.