Those are Islamist terrorists, if the U.S. is waging a war on terrorism there is no better way then to show it's intolerance of any extremists action globally. The longer the U.S. fails to act the more it reinforces the preconceptions that the war in the Middle East was for economic control of the oil trade and the supposed Lithium mines in Afghanistan.
Right now we are all aware the war in those regions were mostly motivated for economic reasons but it'd be nice if the U.S. pretended for a second that it was serious on its war against terrorism instead of letting it slowly spread through Africa as it has been happening.