Terrorist source’s said at least three other Nusra Front commanders were killed in the blast, Reuters reported.
Al-Shami had held the title of general military commander of the group, the Syrian branch of al-Qaeda.
The Syrian news agency Sana, quoting its correspondent, said Abu Hammam al-Shami known as al-Farouq al-Suri and a number of other Nusra leaders had been killed in an army operation targeting the meeting held in the village of Hobait in a rural area of Idlib.
It also cited a military source saying the army had carried out "concentrated strikes" against Nusra and other extremists groups in the Abu al-Dhuhur area, which is to the northeast of Hobait.
Leaders of the Nusra Front are considering cutting their links with al-Qaeda to form a new entity backed by some Persian Gulf states trying to topple President Bashar al-Assad, sources have said.
Insurgent sources had initially said the US-led alliance had killed Abu Humam in an air strike. But a coalition spokesperson said it had not conducted air strikes in the province during the past 24 hours.
The Nusra Front has expanded its hold over Idlib province in recent months, seizing territory from mainstream Syrian "rebel" groups that have received Western backing.
Leaders of the Nusra Front are considering cutting their links with al-Qaeda to form a new entity backed by some Persian Gulf states trying to topple President Bashar al-Assad, sources have said.