Tensions are rising in Afghanistan’s Logar Province today after a pair of US attack helicopters inexplicably attacked an Afghan military checkpoint in broad daylight, killing at least 10 soldiers in a major friendly fire incident.

The helicopters were out on an “advise and assist” mission for Afghan special forces. The US claims the helicopters came under fire, and they responded by attacking the checkpoint, even though it was flying an Afghan flag and was not where the gunfire came from.

That’s the best case story of the incident, though the Afghan forces at the checkpoint didn’t appear to see the putative militants who were firing on the helicopters, which makes attacking the checkpoint even more bizarre.

US officials say the incident is “under investigation,” and while the Afghan government said they believe the attack was probably a mistake, they are keen to get an explanation for the killings.