(CNN) — A US F-15E fighter jet shot down a pro-Syrian regime drone near At Tanf, Syria, on Monday, two US officials told CNN, the third downing of a pro-regime aircraft this month.
The drone was downed just outside the 55 kilometer de-confliction zone, according to the officials.
It was an Iranian-made Shahed 129 and was thought to be armed and in firing range of US troops.
One official said that the drone was shot down because it was “assessed to be a threat.”
The Iranian-made Shahed 129 is the same type that was shot down earlier this month after it dropped a “dud” munition near a patrol being carried out by coalition troops and local forces.
That drone was shot down after it dropped one of several weapons it was carrying near a position where coalition personnel are training and advising partner ground forces in the fight against ISIS.
The incidents mark an escalation in the area around At Tanf — a base near the Syrian-Jordanian border manned by coalition forces that are advising an anti-ISIS Syrian rebel group.
It also comes just days after a US F/A-18 shot down a regime warplane after it dropped bombs near US-backed Syrian Democratic Forces fighting ISIS in the area around Tabqah, Syria, in the country’s north.