frontlines of Syria

A rebel fighter fires his weapon during what the rebels called a battle to unite rebel factions against forces loyal to Syria's President Bashar al-Assad in Jobar, a suburb of Damascus April 21, 2015. REUTERS/Amer Almohibany

A rainbow is seen over an Islamic Ahrar al-Sham fighter in Idlib city March 20, 2015. REUTERS/Khalil Ashawi

Rebel fighters pray before heading towards what they said was an offensive to take control of the northwestern town of Jisr al-Shughour and the surrounding areas, which are controlled by forces loyal to Syria's President Bashar al-Assad, April 20, 2015. REUTERS/Khalil Ashawi

Fighters from Liwa al-Nasr (Victory Brigade) cover a vehicle with mud in order to camouflage it in the Turkmen mountains, Latakia countryside April 18, 2015. REUTERS/Khalil Ashawi

A rebel fighter looks inside a cannon in Idlib city March 23, 2015. REUTERS/Khalil Ashawi

Rebel fighters shop for military outfits and accessories in Aleppo's countryside April 20, 2015. REUTERS/Jalal Al-Mamo

A Free Syrian Army fighter rests beside mortar shells on the outskirts of Doreen town, in Jabal al-Akrad area, northwestern Latakia province, March 8, 2015. REUTERS/Alaa Khweled

A fighter from Liwa al-Nasr (Victory Brigade) fires a mortar shell towards forces loyal to Syria's President Bashar Al-Assad in Turkmen mountains, Latakia countryside April 18, 2015. REUTERS/Khalil Ashawi

Rebel fighters from the Ahrar al-Sham Islamic Movement carry their weapons as they move towards their positions near Morek frontline in the northern countryside of Hama March 16, 2015. REUTERS/Khalil Ashawi

Rebel fighters from the Ahrar al-Sham Islamic Movement sit inside a BMP armored vehicle during what they said was an offensive to take Idlib March 24, 2015. REUTERS/Khalil Ashawi

Rebel fighters of al-Jabha al-Shamiya (the Shamiya Front) walk along orchards on their way back from the frontline against Islamic State fighters on the outskirts of Mare town, north of Aleppo March 24, 2015. REUTERS/Sultan Kitaz

A rebel fighter of al-Jabha al-Shamiya (the Shamiya Front) rests inside a room at al-Amriya frontline in Aleppo March 3, 2015. REUTERS/Hosam Katan

Rebel fighters stand near a vehicle decorated with pictures of Al Qaeda leaders, including Osama bin Laden (R) in Jabal al-Turkman in Latakia province April 20, 2015. REUTERS/Khalil Ashawi

A rebel fighter of al-Jabha al-Shamiya (the Shamiya Front) covered with mud carries his weapon as he sits near the front line with Bashkuwi village, north of Aleppo February 19, 2015. REUTERS/Rami Zayat

Rebel fighters of 'Al-Sultan Murad' brigade use their mobile phones inside a room near the frontline in Handarat area, north of Aleppo March 1, 2015. REUTERS/Hosam Katan

Free Syrian Army fighters of the 101 Infantry Division (the missile and artillery battalion) move toward their positions in Jabal al-Arbaeen, Idlib countryside April 16, 2015. REUTERS/Mohamad Bayoush

A rebel fighter holds an umbrella as he walks in Aleppo's countryside April 20, 2015. REUTERS/Jalal Al-Mamo

Rebel fighters rest inside a room at the old city of Aleppo December 28, 2014. REUTERS/Jalal Al-Mamo

Rebel fighters rest during their fight against forces loyal to Syria's President Bashar al-Assad in the al-Malah area, in Aleppo's countryside December 16, 2014. REUTERS/Sultan Kitaz

A rebel fighter from the Free Syrian Army's Al Rahman legion smokes a cigarette as he stands with his weapon inside a damaged room in Jobar, a suburb of Damascus December 22, 2014. REUTERS/Bassam Khabieh

A rebel fighter pets a dog as a fellow fighter watches in Aleppo January 8, 2015. REUTERS/Jalal Al-Mamo

A rebel fighter rests inside a room at Karm al-Tarab frontline in Aleppo July 30, 2014. REUTERS/Hamid Khatib

A rebel fighter rests after clashes with forces loyal to Syria's President Bashar al-Assad in Ramouseh, an area located beside Aleppo Artillery school December 21, 2014. REUTERS/Sultan Kitaz

A rebel fighter receives a shave from a barber in Karm al-Jabal neighborhood of Aleppo January 5, 2015. REUTERS/Mahmoud Hebbo

A rebel fighter plays football at the Handarat camp frontline, an area located beside Aleppo Central prison July 6, 2014. REUTERS/Hosam Katan

Rebel fighters rest with their weapons inside a safe house at the Handarat camp frontline, an area located beside Aleppo Central prison July 6, 2014. REUTERS/Hosam Katan

A Free Syrian Army fighter plays on a slide in the Jabal al-Akrad area in northwestern Latakia province February 24, 2014. REUTERS/Alaa Khweled

Rebel fighters receive food aid in the old city of Aleppo December 30, 2014. REUTERS/Abdalrhman Ismail

A rebel fighter of al-Badiya brigade in Jaysh al-Islam uses his mobile phone near the frontline of Masasna checkpoint in Hama countryside March 4, 2015. REUTERS/Khalil Ashawi

Free Syrian Army fighters are silhouetted as they stand on one of the frontlines of Wadi Al-Daif camp in southern Idlib countryside September 18, 2014. REUTERS/Khalil Ashawi