Islamist Syrian rebel group Jabhat al-Nusra members gesture while posing on a tank on Al-Khazan frontline
Islamist Syrian rebel group Jabhat al-Nusra members gesture while posing on a tank on Al-Khazan frontline of Khan Sheikhoun, northern Idlib province May 17, 2014. REUTERS/Hamid Khatib (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS CONFLICT)
Islamist Syrian rebel group Jabhat al-Nusra drive a tank on Al-Khazan frontline
Islamist Syrian rebel group Jabhat al-Nusra drive a tank on Al-Khazan frontline of Khan Sheikhoun, northern Idlib province May 17, 2014. REUTERS/Hamid Khatib (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS CONFLICT)
Islamist Syrian rebel group Jabhat al-Nusra members fire their weapon towards what activists said were warplanes loyal to Assad on Al-Khazan frontline
Islamist Syrian rebel group Jabhat al-Nusra members fire their weapon towards what activists said were warplanes loyal to Syria's president Bashar Al-Assad on Al-Khazan frontline of Khan Sheikhoun, northern Idlib province May 17, 2014. REUTERS/Hamid Khatib (SYRIA - Tags: CIVIL UNREST MILITARY POLITICS CONFLICT)
Syrian refugees walk at a Syrian refugee camp north of Aleppo beside the Syrian-Turkish border
Syrian refugees walk at a Syrian refugee camp north of Aleppo beside the Syrian-Turkish border May 17, 2014. REUTERS/Jalal Al-Mamo (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT SOCIETY)
Syrian refugees cook food at a Syrian refugee camp north of Aleppo beside the Syrian-Turkish border
Syrian refugees cook food at a Syrian refugee camp north of Aleppo beside the Syrian-Turkish border May 17, 2014. REUTERS/Jalal Al-Mamo (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT SOCIETY)
Members of Shi'ite group Asaib Ahl al-Haq, who supports Syrian President Bashar al-Assad, carry the coffin of a fellow fighter during his funeral in Najaf
Members of Shi'ite group Asaib Ahl al-Haq, who supports Syrian President Bashar al-Assad, carry the coffin of a fellow fighter during his funeral in Najaf May 17, 2014. The fighter was killed during clashes with the Free Syrian Army in Syria, according to the group. REUTERS/Alaa Al-Marjani (IRAQ - Tags: POLITICS CIVIL UNREST)
Members of Shi'ite group Asaib Ahl al-Haq, who supports Syrian President Assad, carry the coffin of a fellow fighter during his funeral in Najaf
Members of Shi'ite group Asaib Ahl al-Haq, who supports Syrian President Bashar al-Assad, carry the coffin of a fellow fighter during his funeral in Najaf May 17, 2014. The fighter was killed during clashes with the Free Syrian Army in Syria, according to the group. REUTERS/Alaa Al-Marjani (IRAQ - Tags: POLITICS CIVIL UNREST)
Residents look for survivors among the debris and damage at Al-Kallaseh in Aleppo
Residents look for survivors among the debris and damage after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad at Al-Kallaseh in Aleppo May 17, 2014. REUTERS/Hosam Katan (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT)
Residents stand among the debris and damage after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad at Al-Kallaseh in Aleppo
Residents stand among the debris and damage after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad at Al-Kallaseh in Aleppo May 17, 2014. REUTERS/Hosam Katan (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT)
A resident looks for belongings amid the damage after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad at Al-Kallaseh in Aleppo
A resident looks for belongings amid the damage after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad at Al-Kallaseh in Aleppo May 17, 2014. REUTERS/Hosam Katan (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT)