The leader of one of Syria's most powerful rebel groups has been killed along with dozens of other commanders in a bomb attack on a high-level meeting in Idlib province.
Hassan Abboud, the head of the Ahrar al-Sham brigade, was among up to 45 people killed on Tuesday at the meeting in an underground bunker near an ammunition dump outside Ram Hamdan.
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The Idlib meeting brought together Ahrar and a number of other brigades fighting as the Islamic Front alliance, such as Ahrar, Abdallah Azzam and the Iman brigades, to discuss a strategy to fight the Islamic State.
Activists named others killed in the attack: Abu Yazan al-Shami, a member of the Ahrar's shura council, military field commanders Abu Talha al-Askari and Abu Yousuf Binnish, and Abu al-Zubeir, the head of the Iman brigade.
Abu al-Mustafa al-Ambsi, a member of the political bureau of Ahrar, told Al Jazeera that the group was investigating the attack.
"There is a possibility that the meeting was infiltrated and an explosion happened first in the bunker," he said. "Maybe someone planted a device inside because the bunker is at a secret location”.
He said that killing of such an elite group "will only make us more resilient to fight and continue the fight until we liberate our homeland".
It is not known who staged the attack but Islamic State sympathisers hailed the death of Abboud on social media.
Another of Ahrar's leaders, Abu Khaled al-Souri, a close associate with al-Qaeda leaders Osama bin Laden and Ayman al-Zawahiri, was killed by the Islamic State earlier this year.
That assassination caused the schism that pitted the Islamic State group against other rebel factions in Syria.
Ahrar has about 20,000 fighters and is the main force in the Islamic Front alliance, which was formed earlier this year to oppose the Islamic State group.
Ahrar advocates for a state run on Islamic principles, which protects the rights of women and religious and ethnic minorities, and disagrees with the approach of the Islamic State group.
In an interview with Al Jazeera in December 2013, Abboud said he would fight for his rights and dismissed talks in UN-brokered Geneva between the Syrian government and the exiled rebel umbrella Syrian National Coalition
"We see Geneva as a tool of manipulation - to derail the Syrian revolution away from its goals and objectives ... whatever outcome the conference may yield, will be binding on the Syrian National Coalition only.
"For us, we will continue to fight for our revolution until we restore our rights."
However, the rise of the Islamic State after the Geneva talks gave the civil war a new dimension, with Ahrar fighting not only the government but other rebel groups.
Source: Al Jazeera and agencies