A bomb blast has killed several people at a meeting of leaders of key Syrian Islamist insurgent group Ahrar al-Sham.
Some reports say the group's leader Hassan Abboud died in the attack, which activists say was carried out by a suicide bomber.
Ahrar al-Sham is part of the Islamic Front, a coalition of seven Islamist rebel groups.
In February, Ahrar al-Sham blamed the rival Islamic State group for an attack which killed several of its members.
Ahrar al-Sham is one of the biggest rebel groups fighting the government of President Bashar al-Assad.
Two activist groups said a suicide bomber had detonated a vest at the meeting in the town of Ram Hamdan in Idlib province on Tuesday.