Jihadist fighters linked to al Qaida fought with rebels to capture a Syrian military air defence base near Aleppo, reports say.
Videos posted online today apparently shot inside the base say Jabhat al-Nusra took part in the overnight battle for the base. The videos show fighters inspecting lines of large missiles.
Two Aleppo-based activists and Rami Abdul-Rahman, head of the Syrian Observatory for Human Rights, also say Jabhat al-Nusra fought in the battle.
The base's capture is sure to fuel fears that Islamic extremists are playing a greater role after nearly 19 months of unrest in Syria.
Western powers say their presence is a reason not to arm the rebels.
Syrian opposition activists estimate more than 32,000 people have been killed since March 2011 when the uprising against President Bashar Assad's regime began.