Free Syrian Army fighters stand near an ambulance on the eastern edge of the northern Syrian town of al-Bab, Syria, February 27, 2017. (Photo by Khalil Ashawi/Reuters)

Fighters from the Democratic Forces of Syria prepare their weapons in the southwestern countryside of Hasaka, Syria February 17, 2016. Picture taken February 17, 2016. (Photo by Rodi Said/Reuters)

NATO and U.S. flags flutter as U.S. Air Force F-22 Raptor fighter flies over the military air base in Siauliai, Lithuania, April 27, 2016. (Photo by Ints Kalnins/Reuters)

Fighters of the Popular Resistance Committees stand during a graduation ceremony of the affiliate special forces of the Popular Resistance, in Yemen's southwestern city of Taiz October 8, 2015. (Photo by Reuters/Stringer)

Fighters of the pro-government Popular Resistance Committees militia carry a cannon as they transport it in parts to Yemen's southwestern war-torn city of Taiz December 26, 2015. (Photo by Reuters/Stringer)

People run in panic after a coalition airstrike hit Islamic State fighters positions in Tahrir neighbourhood of Mosul, Iraq, November 17, 2016. (Photo by Goran Tomasevic/Reuters)

A Cholita (Andean woman) fighter makes a key to their opponent during a wrestling session at the Havana Hotel Cholet in El Alto, outskirts in La Paz, Bolivia on June 29, 2018. (Photo by David Mercado/Reuters)