Story highlights Two US aircraft were dispatched as a "show of force" to get the Syrian vehicles to turn around

An official said at this time it is not clear if the strike was intended as a warning

Washington (CNN) US-led coalition aircraft bombed pro-Syrian regime forces Thursday that "were advancing well inside an established de-confliction zone," according to a statement issued by Operation Inherent Resolve, the official name for the coalition fighting ISIS.

The statement said the pro-regime militias "posed a threat to US and partner forces at At Tanf," a remote base in southern Syria near the Syria-Jordan-Iraq border that coalition advisers have used to train "Vetted Syrian Opposition" to aid the fight against ISIS.

Two US aircraft were dispatched as a "show of force" to get the Syrian vehicles to turn around, according to a US official.

The official statement said that the vehicles did not stop despite the show of force and warning shots.

A second US defense official said an airstrike hit the convoy after the vehicles continued toward the base, striking an enemy tank and bulldozer, or front loader-type vehicle.

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