A bomb attack killed at least 14 Syrian insurgents at a headquarters for the powerful Islamist Ahrar al-Sham group on Sunday, the Syrian Observatory for Human Rights monitoring group said.
Two blasts including at least one suicide attacker hit the base in a village east of Saraqeb in Idlib province, the British-based Observatory reported.
There was no immediate claim of responsibility for the blast.
Photos circulated on social media showed bloodied corpses and a blackened motorbike outside a small building in the village. The pictures could not immediately be verified.
Idlib is a rebel stronghold, but some insurgent factions have fought among themselves this year, including in clashes that pitted groups aligned with Ahrar al-Sham against groups that joined the al Qaeda-linked Hayat Tahrir al-Sham alliance.
Syrian government forces have taken advantage of rebel infighting, particularly a separate spat further south near Damascus, to recapture territory from insurgents in the six-year conflict.