A young Free Syrian Army fighter holds a rifle in Haresta neighbourhood of Damascus January 16, 2013. (Photo by Goran Tomasevic/Reuters)

A Russian air force technician reports to a pilot that a bomber is ready for a combat mission at Hemeimeem air base in Syria Wednesday January 20, 2016. Russian warplanes have flown over 5,700 combat missions since Moscow launched its air campaign in Syria on September 30, 2015. (Photo by Vladimir Isachenkov/AP Photo)

This file photo provided on Sunday February 15, 2015 by the Syrian anti-government activist group Aleppo Media Center (AMC), which has been authenticated based on its contents and other AP reporting, shows Syrian rebels firing locally made shells against the Syrian government forces, in Aleppo, Syria. (Photo by AP Photo/Aleppo Media Center)

A Russian Sukhoi Su-25 fighter jet takes off during the withdrawal of Russian troops from Syria at Hmeymim airbase, Syria, March 16, 2016. (Photo by Vadim Grishankin/Reuters/Russian Ministry of Defence)

A participant covered in coloured powder gestures as she stands near a Syrian army soldier during “I Love Damascus” marathon at Umayyad Square in Damascus, Syria October 7, 2016. (Photo by Omar Sanadiki/Reuters)

A girl wearing a butterfly headband poses for a picture near damaged buildings in the rebel held besieged city of Douma, in the eastern Damascus suburb of Ghouta, Syria January 19, 2017. (Photo by Bassam Khabieh/Reuters)

A man carries an injured woman in a site hit by what activists said were airstrikes carried out by the Russian air force in the rebel-controlled area of Maaret al-Numan town in Idlib province, Syria January 9, 2016. At least 70 people died in what activists said where four vacuum bombs dropped by the Russian air force in the town of Maaret al-Numan; other air strikes where also carried out in the towns of Saraqib, Khan Sheikhoun and Maar Dabseh, in Idlib. (Photo by Khalil Ashawi/Reuters)

Thai classical dancers perform for Phra Phrom, the Thai interpretation of the Hindu god Brahma, at the Erawan Shrine in Bangkok, Thailand, Friday, September 4, 2015. Thai authorities unveiled the restored centerpiece Friday of the Erawan Shrine, in the latest bid to restore confidence among Bangkok's tourism and business communities almost three weeks after a deadly bombing. (Photo by Sakchai Lalit/AP Photo)