Rebel fighting turns inward in Syria.
New amateur video appears to show rebel factions battling fighters from the Islamic State in Iraq and the Levant, a powerful al Qaeda-linked group.
The gun battles are said to have taken place in Aleppo, a northern Syrian city captured by rebels 18 months ago.
Another video appears to show a rebel fighter with an anti-aircraft machine gun, purportedly seized from the Islamist forces.
The video, which cannot be independently verified by Reuters, comes as the U.S. is raising the prospect that Iran, the Shi'ite power long at odds with Washington, could play some role in this month's Syrian peace talks.
More video appears to show rebels gaining control of a stronghold belonging to the Islamic State in Iraq and the Levant.
Activists say the al Qaeda affiliate rebel group is withdrawing from certain areas.
Activists described the move as a tactic to end clashes between Syrian- and foreign-led opponents of President Bashar al-Assad.