The explosion took place in the northwestern section of Syria and killed 12 including Hassan Aboud the leader of Ahrar al-Sham. The group is part of the Islamic Front, an alliance that has been fighting both the Syrian army as well as the Islamic State.
A human right organization said that an explosion had killed 28 commanders of Ahrar al-Sham, dealing it a huge blow. The group is said to have been given funds by Gulf States.
In a statement released on a video, the group said Hashem al-Sheik had been appointed the leader and that the new military chief was Abu Saleh Tahan. It said it would continue fighting the Syrian government and the Islamic State.
Close to 50 of the leaders of the group had been at a home when the huge blast was set off in the meeting. No one claimed responsibility for the bombing.
Some observers described the incident on Tuesday as an attack that used gas. Abu Baraa a figure with the rebels said one doctor who had examined bodies from the incident there had been little sign of any external injuries.
The doctor said bodies had frothing mouths and fluids draining from the noses and eyes.
The observer said the attack was highly sophisticated in a location that had been secure.
During this past January, a senior leader of Ahrar al-Sham was killed during a suicide attack. The leader had fought alongside Osama bin Laden the founder of al-Qaeda.
The militant group Islamic State denied involved in the attack after being accused of carrying it out.
At one point, Ahrar al-Sham, which want Sharia law in all of Syria, was considered amongst the strongest groups of insurgents during the civil war.
However, that title has been taken by Islamic State, which has seized large swathes of land in both Iraq and Syria.