A blast targeting senior members of al Qaeda's official Syrian wing, the Nusra Front, killed the group's General Military Commander Abu Humam al-Shami on Thursday, two insurgent sources told Reuters.
Al-Shami is one of the most senior Nusra Front figures to be killed since it formed in 2012 and has fought in Afghanistan, Iraq and Syria, the sources said. They said the explosion was caused by a US-led coalition air strike that hit a high-level Nusra Front meeting in the northwestern province of Idlib.
The United States has carried out strikes against one of Nusra's jihadi rivals, Islamic State, in Iraq since July and in Syria since September. It has also targeted Nusra fighters in Syria.
The Nusra Front has fought western-backed rebels this year, seizing their territory and forcing them to disarm so as to consolidate its power in northern Syria.
Hazzm, one of the last remnants of non-jihadist opposition to President Bashar al-Assad in northern Syria, dissolved itself last week after weeks of fighting with the Nusra Front.
After Thursday's attack, the Nusra Front told its members not to provide information to the media, the sources said.
The weakness of the mainstream Syrian opposition and the growing power of the Nusra Front and Islamic State has complicated diplomatic efforts to end the Syrian conflict that has killed around 200,000 people.