The Pentagon says the military is too stretched to both fight insurgents and prepare for war with great world powers.
The Somalis boarded a flight to the war-torn country on Thursday, but the plane only made it as far as Senegal. Immigration officials cited logistical issues.
The United States Africa Command said the airstrike was carried out 125 miles northwest of Mogadishu, the Somali capital.
The Trump administration has redoubled its campaign to defeat the Qaeda-backed Shabab, but the group has proved to be a potent and resilient killing force.
A pair of strikes against the Islamic State marked an expansion of the American-led air campaign as the group was losing ground in Syria and Iraq.