US “training” operations in Niger took a turn for the deadly on Wednesday, when a joint patrol sustained substantial casualties in an ambush by unspecified “enemies” near the Niger-Mali border. These are the first US combat deaths recorded in Niger, with another US soldier killed in a vehicle accident earlier this year.

The incident was initially reported to have left three US soldiers killed and two wounded. Niger has since confirmed that four Nigerien soldiers were killed and eight wounded. Reports are that a fourth US soldier has since been found dead after the incident.

The incident is raising a lot of questions, however, because US commanders had been telling everyone involved that the patrols were “low risk” and that there was little hostile activity in the area.

Now officials are trying to figure out what happened, and whether patrols became so predictable that the troops in the country made themselves a target in the area. For now, even who carried out the attack is subject to speculation.

The most likely candidate is al-Qaeda in the Islamic Maghreb (AQIM), which is known to operate in the border area. Boko Haram, however, is also active in the region, and it would not be unheard of for them to carry out such an ambush.

The fact that there were two potential attacking groups at all underscores just how “low-risk” the mission wasn’t, however, and the attack forced the US not only to confirm combat deaths, but also to confirm that their operations in Niger were more than just training.