Friday’s attack also follows the Oct. 4 ambush in Niger that killed four American soldiers, their interpreter, and four Nigerien troops. That ambush has opened a debate in Washington over the American military mission in Africa. The Pentagon has carefully monitored the spread of radical Islamic jihad across Africa but insisted that American troops are there to train and partner with local forces, not necessarily to fight.
Over the past year, American military officials have expressed new concerns about the Shabab, which was responsible for one of the deadliest terrorist attacks on African soil when it struck a popular mall in Nairobi in 2013. Officials worry the extremist group is in the midst of a resurgence after losing much of the territory it once held in Somalia and many of its fighters in the last several years.
In September 2014, American officials said they believed a drone strike crippled the group by killing its leader, Ahmed Abdi Godane, who at the time was one of the most wanted men in Africa. That strike was followed by another one in March 2015, when Adan Garar, a senior member of the Shabab, was killed in his vehicle.
But the Shabab no longer appears to be crippled by the killings of Mr. Godane and Mr. Garar. In the past two months, Shabab militants have claimed responsibility for attacks that have killed more than 150 people, including Kenyan soldiers stationed at a remote desert outpost and beachcombers in Mogadishu, the capital.
Two months ago, the group carried out multiple coordinated attacks against African Union peacekeeping forces, killing dozens of Ugandan soldiers.
On Monday, The New York Times reported that a sweeping Pentagon review of elite United States commando missions is likely to result in a sharp cut — by as much as half over the next three years — in Special Operations forces in Africa.
Defense Secretary Jim Mattis and Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, have ordered the military’s Special Operations and Africa commands to present a range of options by mid-June to balance rising security challenges — which also include North Korea and Iran — with vital counterterrorism operations.
More than 7,300 Special Operations troops are working around the world, many of them conducting shadow wars against terrorists in Yemen, Libya, Somalia and other hot spots.