The terrorist group seized control of Tabqa air base on Sunday from forces loyal to President Bashar al-Assad.
At least 250 Syrian soldiers were reportedly executed on Wednesday, IS claimed on one of its official websites. Video footage purportedly of the soldiers shows large groups of men forced to jog in their underwear and later images of numerous corpses in similar undress lying side by side in a desert area.
According to the London-based Syrian Observatory for Human Rights, 200 Syrian soldiers and 346 IS fighters were killed in Sunday's battle for control of the air base.
2014: The Year in Music [PHOTOS]