What happened

Syrian government forces, backed by Russian air power and Hezbollah fighters, broke a nearly three-year Islamic State siege of the Deir ez-Zor military airbase on 9 September 2017, according to Syrian state media, which said troops advancing from a cemetery southwest of the city linked up with the besieged garrison to establish a corridor through IS-held territory. Damascus said it would use the airbase as a launching pad to recapture remaining IS-held areas toward the Iraqi border, in a province containing some of Syria's largest oil fields. The advance coincided with a separate, competing offensive by the US-backed Syrian Democratic Forces in the same region, raising concerns at the time about potential friction between the two anti-IS campaigns. The reviewed reporting (Al Jazeera; France 24) did not provide specific casualty figures for the relief operation.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.