A rebel sniper fires at government forces.
This is the Syrian city of Aleppo and video obtained by Reuters appears to show the Free Syrian Army battling forces loyal to President Bashar al-Assad.
Challenging Assad's control of the capital Damascus and Syria's largest city Aleppo has upped the ante in recent days.
But Assad has vowed to fight to the death in a conflict that has killed some 38,000 people and risks sucking in other countries.
The chief international mediator said on Thursday Russia and the United States would seek a "creative" solution to the crisis, suggesting coordination between the major powers might be possible after months of disagreement.
Rebels have made advances on Damascus and taken several military bases in recent weeks but Assad's superior military power continues to dominate, flattening opposition-held areas with aerial and artillery strikes.
Syrian rebels prepare for battle in Aleppo (1:09)
Dec. 7 - Free Syrian Army fighters attack Aleppo Air Force Intelligence compound, according to video obtained by Reuters. Lily Grimes reports. ( Transcript )