On Friday, a US drone strike in southern Somalia killed 18 people. US African Command (AFRICOM) claimed that all of the slain were al-Shabaab fighters, and that the attack was conducted in self-defense.
Their statement claims that US and “allied forces” came under fire in an area near Kismayo. The US called in the drone strike after this fire happened. They did not say who the allies were, but generally this means Somali troops inside Somalia.
Details on who the US actually attacked and where are unclear, as the Aftricom statement declares everyone al-Shabaab, but provides no indication that they were either the same fighters attacking the US troops, or how they were identified after the fact.
In general, the claims of self defense are made as a legal justification for US airstrikes in countries like Somalia, as opposed to providing a positive identification of an enemy. As is so often the case, the “attack” on US and allied troops did not involve a single casualty, and may just as well not have happened.