American analysts estimate that Al Shabab command anywhere from 5,000 to 10,000 fighters. Under Mr. Mohamed, their bombs have grown more sophisticated and powerful.

The group uses its hold on Mogadishu port to smuggle in large volumes of explosive materials and Chinese-made trigger devices, two U.S. officials said. In October 2020, Somali authorities intercepted 79 tons of sulfuric acid, an ingredient in roadside bombs.

In January, a bomb struck an armored convoy with American-trained Danab commandos, traveling toward Baledogle, a base 70 miles from Mogadishu.

The blast badly wounded the Danab commander, Maj. Ahmed Abdullahi, who was airlifted to Turkey, and killed a South African employee of Bancroft Global Development, an American contractor that recruits and trains Danab fighters. The South African, Stephen Potgieter, was the seventh Bancroft employee to die in Somalia since 2009, said Michael Stock, the company’s chief executive.

Mr. Mohamed’s growing reputation for chaos and bloodshed have made him a highly respected leader inside Shabab ranks, Somali and Western officials said.

To those pursuing him, he is an elusive figure, always out of reach.

American Mistakes

As in Afghanistan, America’s campaign in Somalia has been undermined by its own deadly misfires.

After an American missile struck a farmhouse near Jilib, southern Somalia, in February 2020, the military said it had killed a “terrorist.” Months later the military admitted that it had, in fact, killed a 17-year-old schoolgirl named Nurto Kusow Omar.