Jabhat Fateh al-Sham commander Abu Omar Sarakeb reported killed in air strike in Syria's Aleppo province
The top military commander of the Army of Conquest, the largest Syrian rebel alliance, was killed in an air strike on a meeting of the group's leaders, militant sources said on Thursday.
Jabhat Fateh al-Sham, formally the Nusra Front, announced on Twitter "the martyrdom" of commander Abu Omar Sarakeb during an air strike in Syria's Aleppo province.
The nationality of the jets that hit the location was not immediately known, but a rebel source said initial information suggested it was most likely a US aircraft.
Jets from the Russian and Syrian air forces are also launching raids in the area.
Since the US-led coalition was launched, air strikes have targeted Nusra Front figures in Syria, killing scores. But this would mark the first time a key figure has been targeted since the group's name change.
Sarakeb was a founding member of Nusra Front, al-Qaeda's powerful Syrian branch, and had been among militants who fought US forces in Iraq after the invasion in 2003, before returning to Syria.
Along with other leaders, he set up the Army of Conquest - a military alliance of rebel groups that last year drove the Syrian army from the northwestern city of Idlib at the height of rebel advances.
The major Russian military campaign at the end of last year turned the tide in Syrian President Bashar al-Assad's favour and thwarted the rebel's rapid gains that brought them close to Assad's coastal stronghold of Latakia.
Another rebel source told Reuters the militants were present in a secret hideout in the village of Kafr Naha when the raid took place. The leader of the group Abu Mohammad al-Jolani was apparently not at the meeting.
Few other details emerged of the strike, but a photo of another top leader known as Abu Muslim al-Shami circulated on social media showing him alive in an effort to refute reports he had also been killed.
The Nusra Front announced last July it was ending its relationship with al-Qaeda to remove a pretext used by world powers to inflict civilian casualties.
The move appeared to be an attempt to appeal to Syrians who have long had deep misgivings about Nusra's links with al-Qaeda and the presence of foreign fighters in its ranks.
The move was dismissed by Washington, which said it did not change its stance on the organisation that is listed as a terrorist group and remained a fair target. Washington said altering the name of the group did not signal a shedding of its hardline al-Qaeda-style ideology.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov have been trying to reach a deal on deeper cooperation between the US and Russian militaries against groups operating in Syria, particularly Islamic State and the former Nusra Front.
One of the complications is that former Nusra operates side by side with Western-backed moderate Free Syrian Army rebel groups in major frontlines against the Syrian army, which is aided by heavy Russian air power and fighters from Iran-backed militias.