A general view shows the Zeno street frontline in Aleppo November 18, 2014. (Photo by Hosam Katan/Reuters)

Rebel fighters carry their weapons as they head towards their positions near the frontline against forces loyal to Syria's president Bashar Al-Assad in the Jabal al-Akrad area in Syria's northwestern Latakia province November 25, 2014. (Photo by Alaa Khweled/Reuters)

Rebel fighters aim their weapons as they take positions at the frontline against forces loyal to Syria's President Bashar al-Assad in Maysaloun neighborhood in the old city of Aleppo November 24, 2014. (Photo by Abdalrhman Ismail/Reuters)

Rebel fighters carry their weapons as they stand along an alleyway at the frontline against forces loyal to Syria's President Bashar al-Assad in Maysaloun neighborhood in the old city of Aleppo November 24, 2014. (Photo by Abdalrhman Ismail/Reuters)

A fighter from the Al-Mujahideen army, which operates under the Free Syrian Army, walks through a hole in the wall on the Zeno street frontline in Aleppo November 18, 2014. (Photo by Hosam Katan/Reuters)

Rebel fighters take up position behind piles of sandbags on the Karm al-Tarab frontline, next to Aleppo International airport November 23, 2014. (Photo by Abdalrhman Ismail/Reuters)

A Free Syrian Army fighter prepares a locally made shell before firing it towards forces loyal to Syria's President Bashar al-Assad in Bani Zeid neighborhood, Aleppo November 10, 2014. (Photo by Abdalrhman Ismail/Reuters)

Rebel fighters launch a locally made weapon on the Karm al-Tarab frontline towards forces loyal to Syria's President Bashar al-Asaad, at Aleppo International airport November 23, 2014. (Photo by Abdalrhman Ismail/Reuters)

Al-Mujahideen army fighters, which operates under the Free Syrian Army, sit in shooting positions inside a damaged room during clashes with forces loyal to Syria's President Bashar al-Assad on the Zeno street frontline in Aleppo November 18, 2014. (Photo by Hosam Katan/Reuters)

Mariam, a 9 year-old girl, carries her brother as she stands at the door of an underground ancient cemetery in Jabal al-Zawiya in the southern countryside of Idlib, November 26, 2014. Residents are using ancient caves and cemeteries as underground shelters to hide in during shelling from forces loyal to President Bashar al-Assad. Picture taken November 26, 2014. (Photo by Khalil Ashawi/Reuters)

Mariam, a 9-year-old girl, carries her brother as she stands with other children at an underground ancient cemetery in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

A displaced girl poses inside an underground cave in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

A displaced woman, standing with children, gestures as she talks inside an underground cave in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

A displaced girl stands in front of a tent that was erected atop of an underground cave in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

Reham (L), a 13-year-old displaced girl, stands on a hill on top of underground caves in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

Displaced civilians walk out of an underground cave in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

Um Mohamed, a 87-year-old displaced woman, sits inside a tent that was erected atop of an archaeological hill in Jabal al-Zawiya in the southern countryside of Idlib November 26, 2014. (Photo by Khalil Ashawi/Reuters)

Men search under the rubble as others inspect a site hit by what activists said were air strikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

People run amid smoke from a site hit by what activists said were air strikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

A man leans on an ambulance as people search for survivors under rubble at a site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad, in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

A man runs while pointing at a site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

A man makes his way through rubble at a site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

Men clear a damaged site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

A girl reacts as a man holds her hand at site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad in Raqqa, eastern Syria, which is controlled by the Islamic State November 27, 2014. (Photo by Nour Fourat/Reuters)

Fighters from the Noureddine Zanki movement, which operates under the Free Syrian Army, prepare an improvised explosive to fire towards forces loyal to Syria's President Bashar al-Assad at the frontline in Aleppo's al-Rashideen neighborhood November 27, 2014. (Photo by Hosam Katan/Reuters)

Fighters from the Noureddine Zanki movement, which operates under the Free Syrian Army, prepare an improvised explosive to fire towards forces loyal to Syria's President Bashar al-Assad at the frontline in Aleppo's al-Rashideen neighbourhood November 27, 2014. (Photo by Hosam Katan/Reuters)

Fighters from the Noureddine Zanki movement, which operates under the Free Syrian Army, rest inside a room near the frontline against forces loyal to Syria's President Bashar al-Assad in Aleppo's al-Rashideen neighbourhood November 27, 2014. (Photo by Hosam Katan/Reuters)

A Syrian refugee girl stands with her brother near their tent at a refugee camp in Zahle in the Bekaa valley November 27, 2014. (Photo by Jamal Saidi/Reuters)

Fighters from the Noureddine Zanki movement, which operates under the Free Syrian Army, take positions as one of them aims his weapon at the frontline against forces loyal to Syria's President Bashar al-Assad in Aleppo's al-Rashideen neighbourhood November 27, 2014. (Photo by Hosam Katan/Reuters)

An elderly Syrian refugee woman sits near her tent at a refugee camp in Zahle in the Bekaa valley November 27, 2014. (Photo by Jamal Saidi/Reuters)

Syrian refugees stand on muddy ground at a refugee camp in Zahle in the Bekaa valley November 27, 2014. (Photo by Jamal Saidi/Reuters)

A Syrian refugee girl stands near her tent at a refugee camp in Zahle in the Bekaa valley November 27, 2014. (Photo by Jamal Saidi/Reuters)