The Kurdish dominated Syrian Democratic Forces (SDF) are reporting today that US troops have taken over control of the Rmeilan airfield in northeastern Syria’s Hasakeh Province, the first US military base inside Syria.

The SDF reported that the Kurdish YPG, their largest faction, previously controlled the base and handed sole control over it to the US, as a route for the US to bring them weapons and to launch warplanes from.

Rmeilan Airport is not a military airfield by design, and was primarily for crop-dusting and agriculture. It is unclear, then, the extent to which it’ll really be used by the US as a base for warplanes. The US generally launches such planes from Turkey, though Turkey has loudly objected to the US aiding the Kurds.

Some reports from the Syrian Observatory for Human Rights suggest that work is underway to expand the runway, and that US attack helicopters have been seen going in and out of the base for weeks.

Pentagon spokesman Col. Steve Warren confirmed that there is an operation “ongoing” in the area, but refused to discuss the matter, citing the “special nature” of the US ground troops who are deployed in Syria. Officials previously confirmed a handful of troops were sent to Syria, but never suggested they were going to establish their own bases.

The operation appears legally dicey, at best, as while the base was nominally under the control of the Kurdish YPG, who are closely allied to the US, the Obama Administration has refused all coordination with the Syrian government, and certainly doesn’t have Syrian permission to establish military bases on Syrian soil.