"Abu Firas al-Suri, his son and at least 20 jihadists of Al-Nusra and Jund al-Aqsa and jihadists from Uzbekistan were killed in strikes on positions in Idlib province," Syrian Observatory for Human Rights chief Rami Abdel Rahman told AFP.
It was not immediately clear if the raids were carried out by Syrian regime warplanes or their Russian allies.
Abdel Rahman said Suri was meeting with other leading jihadists in Kafar Jales when the raids struck and that two other Al-Nusra and Jund al-Aqsa targets were also attacked.
On Wednesday, a drone strike near IS's de facto Syrian capital Raqa killed a jihadist commander, according to the Observatory, in the latest in a series of blows to the jihadists in recent weeks.