American officials said the White House had quietly broadened the president’s authority for the use of force in Somalia by allowing airstrikes to protect American and African troops as they combat fighters from the Shabab, a Somali-based militant group that has proclaimed allegiance to Al Qaeda.
In its public announcements, the Pentagon sometimes characterizes the operations as “self-defense strikes,” though some analysts have said this rationale has become a self-fulfilling prophecy. It is only because American forces are now being deployed on the front lines in Somalia that they face imminent threats from the Shabab.
America’s role in Somalia has expanded as the Shabab have become bolder and more cunning. The group has attacked police headquarters, bombed seaside restaurants, killed Somali generals and stormed heavily fortified bases used by African Union troops. In January, Shabab fighters killed more than 100 Kenyan troops and drove off with their trucks and weapons.
The group carried out the 2013 attack at the Westgate mall, which killed more than 60 people and wounded more than 175 in Nairobi, Kenya. More recently it has branched into more sophisticated forms of terrorism, including nearly downing a Somali airliner in February with a bomb hidden in a laptop computer.
About 200 to 300 American Special Operations troops work with soldiers from Somalia and other African nations like Kenya and Uganda to carry out more than a half-dozen raids per month, according to senior American military officials. The operations are a combination of ground raids and drone strikes.
The Navy’s classified SEAL Team 6 has been heavily involved in many of these operations.
Once ground operations are complete, American troops working with Somali forces often interrogate prisoners at temporary screening facilities, including one in Puntland, a state in northern Somalia, before the detainees are transferred to more permanent Somali-run prisons, American military officials said.
The Pentagon has acknowledged only a small fraction of these operations. But even the information released publicly shows a marked increase this year. The Pentagon has announced 13 ground raids and airstrikes thus far in 2016 — including three operations in September — up from five in 2015, according to data compiled by New America, a Washington think tank. The strikes have killed about 25 civilians and 200 people suspected of being militants, the group found.
The strikes have had a mixed record. In March, an American airstrike killed more than 150 Shabab fighters at what military officials called a “graduation ceremony,” one of the single deadliest American airstrikes in any country in recent years. But an airstrike last month killed more than a dozen Somali government soldiers, who were American allies against the Shabab.
Outraged Somali officials said the Americans had been duped by clan rivals and fed bad intelligence, laying bare the complexities of waging a shadow war in Somalia. Defense Secretary Ashton B. Carter said the Pentagon was investigating the strike.
Some experts point out that with the administration’s expanded self-defense justification for airstrikes, a greater American presence in Somalia would inevitably lead to an escalation of the air campaign.
“It is clear that U.S. on-the-ground support to Somali security forces and African Union peacekeepers has been stepped up this year,” said Ken Menkhaus, a Somalia expert at Davidson College. “That increases the likelihood that U.S. advisers will periodically be in positions where Al Shabab is about to launch an attack.”
Peter Cook, the Department of Defense spokesman, wrote in an email, “The DoD has a strong partnership with the Somali National Army and AMISOM forces from Djibouti, Ethiopia, Kenya, Uganda and Burundi operating in Somalia. They have made steady progress pressuring Al Shabab.”
The escalation of the war can be seen in the bureaucratic language of the semiannual notifications that Mr. Obama sends to Congress about American conflicts overseas.
The Somalia passage in the June 2015 notification is terse, saying American troops “have worked to counter the terrorist threat posed by al-Qa’ida and associated elements of al-Shabaab.”
In June, however, the president told Congress that the United States had become engaged in a more expansive mission.
Besides hunting members of Al Qaeda and the Shabab, the notification said, American troops are in Somalia “to provide advice and assistance to regional counterterrorism forces, including the Somali National Army and African Union Mission in Somalia (AMISOM) forces.”
American airstrikes, it said, were carried out in defense of the African troops and in one instance because Shabab fighters “posed an imminent threat to U.S. and AMISOM forces.”
At an old Russian fighter jet base in Baledogle, about 70 miles from the Somali capital, Mogadishu, American Marines and private contractors are working to build up a Somali military unit designed to combat the Shabab throughout the country.
Soldiers for the military unit, called Danab, which means lightning in Somali, are recruited by employees of Bancroft Global Development, a Washington-based company that for years has worked with the State Department to train African Union troops and embed with them on military operations inside Somalia.
Michael Stock, the company’s founder, said the Danab recruits received initial training at a facility in Mogadishu before they were sent to Baledogle, where they go through months of training by the Marines. Bancroft advisers then accompany the Somali fighters on missions.
Mr. Stock said the goal was to create a small Somali military unit capable of battling the Shabab without repeating the mistakes in Afghanistan and Iraq, where the United States spent hundreds of millions of dollars trying to build up large armies.
Still, American commanders and their international partners are considering a significant expansion of the training effort to potentially include thousands of Somali troops who would protect the country when African Union forces eventually left the country.