Fighters from the Free Syrian Army's Tahrir al Sham brigade use a shotgun to fire an improvised grenade at Syrian Army soldiers in the Arabeen neigbourhood of Damascus February 9, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS TPX IMAGES OF THE DAY CONFLICT)

A fighter from the Free Syrian Army's Tahrir al Sham brigade runs across a street, in front of a Syrian Army base, in the Arabeen neigbourhood of Damascus February 9, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS TPX IMAGES OF THE DAY CONFLICT)

A Free Syrian Army fighter walks through a dust-filled stairwell after a comrade fired a B-10 recoilless gun at Syrian Army soldiers in the Haresta neighbourhood of Damascus February 7, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

A Free Syrian Army fighter carries ammunition for a B-10 recoilless gun in the Haresta neighbourhood of Damascus February 7, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

A Free Syrian Army fighter holds the head of a mannequin up to a hole in a wall of a Syrian Army base to attract and locate a sniper during heavy fighting in the Arabeen neighbourhood of Damascus February 3, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST)

A Free Syrian Army fighter fires a rifle through a hole in a wall of a Syrian Army base, just before he was shot in the head by a sniper, during heavy fighting in the Arabeen neighbourhood of Damascus February 3, 2013. TREUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST CONFLICT TPX IMAGES OF THE DAY)

A Free Syrian Army fighter, who was wounded by a hand grenade, lies on the ground during heavy fighting outside a Syrian Army base in the Arabeen neighbourhood of Damascus February 3, 2013. The hand grenade was thrown by Syrian Army soldiers and wounded four Free Syrian Army fighters. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST CONFLICT)

A Free Syrian Army fighter gestures as he checks Syrian Army positions during clashes in the Haresta neighbourhood of Damascus February 1, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

A Free Syrian Army fighter prays in Haresta neighbourhood of Damascus January 31, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT RELIGION CIVIL UNREST POLITICS)

Fighters from the Free Syrian Army's Tahrir al Sham brigade look at a Syrian Army base in the Arabeen neigbourhood of Damascus February 9, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS CONFLICT)

A Free Syrian Army fighter walks after firing a B-10 recoilless gun at Syrian Army soldiers in the Haresta neighbourhood of Damascus February 7, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

Free Syrian Army fighters walk through a dust-filled stairwell after a comrade fired a B-10 recoilless rifle at Syrian Army soldiers in the Haresta neighbourhood of Damascus February 7, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)FOR BEST QUALITY IMAGE SEE:GM1E93B0OL401

A Free Syrian Army fighter wounded by a sniper is carried by other fighters outside a Syrian Army base during heavy fighting in the Arabeen neighbourhood of Damascus February 3, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

A Free Syrian Army fighter, who was wounded by a sniper, holds his forehead on a wall of a Syrian Army base during heavy fighting in the Arabeen neighbourhood of Damascus February 3, 2013. TREUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST CONFLICT)

A Free Syrian Army fighter gestures as he checks Syrian Army positions during clashes in the Haresta neighbourhood of Damascus February 1, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

Free Syrian Army fighters run for cover as a tank shell explodes on a wall during heavy fighting in the Ain Tarma neighbourhood of Damascus January 30, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

Free Syrian Army fighters run for cover as a tank shell explodes on a wall during heavy fighting in the Ain Tarma neighbourhood of Damascus January 30, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

A wounded Free Syrian Army fighter cries after hearing that his friend died in a mission in the Ain Tarma neighbourhood of Damascus January 30, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

An injured Free Syrian Army fighter holds his head soon after a tank shell exploded on a wall during heavy fighting in the Ain Tarma neighbourhood of Damascus January 30, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS)

A Free Syrian Army fighter gestures in front of a burning barricade during heavy fighting in the Ain Tarma neighbourhood of Damascus January 30, 2013. . REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS TPX IMAGES OF THE DAY)

A Free Syrian Army fighter fires a rocket propelled grenade (RPG) during heavy fighting in the Ain Tarma neighbourhood of Damascus January 30, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CONFLICT CIVIL UNREST POLITICS TPX IMAGES OF THE DAY) FOR BEST QUALITY IMAGE SEE LM2EA2E0VRG01

A fighter from the Free Syrian Army's Tahrir al Sham brigade takes a break during heavy fighting in Mleha suburb of Damascus, January 25, 2013. REUTERS/Goran Tomasevic

A fighter from the Free Syrian Army's Tahrir al Sham brigade takes a break inside a house during heavy fighting in Mleha suburb of Damascus January 26, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

A fighter from the Free Syrian Army's Tahrir al Sham guards a street as other fighter runs into a building during heavy fighting in Mleha suburb of Damascus January 26, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

Fightesr from the Free Syrian Army's Tahrir al Sham brigade take cover during heavy fighting in Mleha suburb of Damascus, January 26, 2013. REUTERS/Goran Tomasevic

An unexploded mortar shell fired by Syrian Army is seen in Mleha suburb of Damascus, January 25, 2013. REUTERS/Goran Tomasevic

A fighter from the Free Syrian Army's Tahrir al Sham brigade eats his breakfast as another fighter runs carrying yogurts for their comrades during heavy fighting in Mleha suburb of Damascus January 25, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

A fighter from the Free Syrian Army's Tahrir al Sham brigade runs as he carries yogurt for his comrades during heavy fighting in Mleha suburb of Damascus January 25, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

A Free Syrian Army fighter uses a shotgun to fire a homemade grenade at Syrian Army soldiers during a fight in the Arabeen neighbourhood of Damascus January 24, 2013. REUTERS/Goran Tomasevic (SYRIA - Tags: CIVIL UNREST POLITICS)

A Free Syrian Army fighter stands in front of the building destroyed by Syrian Army air strikes in the Arabeen neighbourhood of Damascus January 24, 2013. REUTERS/Goran Tomasevic