The US has tried to bolster the Afghan government in Helmand Province with air support in their fighting against the Taliban, but the support appears to have gone horribly wrong today, as a US drone attacked and killed at least 15 Afghan police.

The airstrike was targeting what the US thought was a Taliban compound in Helmand’s Gereshk District, but was actually a site used by Afghan security forces to meet and plan operations against the Taliban. A number were inside when the US attacked.

Death tolls still aren’t totally finalized, but Helmand Governor Hayatullah Hayat confirmed that two top police commanders were among the slain. The Afghan government suggested no soldiers were among the slain, and that it was only the local and provincially-provided police forces that sustained casualties.

The Pentagon expressed condolences for “the unfortunate incident,” but provided no indication as to why they attacked the compound, simply terming the attack part of a “US-supported operation.” Either way, this likely derails the anti-Taliban operation that was ongoing in the district.