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The December 15 strike occurred about 30 miles (50 kilometers) outside the southern coastal city of Kismayo, the US military's Africa Command said in a statement.
"We assess no civilians were killed in the strike," the statement read.
The Shabaab has been fighting to overthrow successive internationally backed governments in Mogadishu since 2007 and frequently deploys car and truck bombs against military, government and civilian targets.
The United States -- which supports Somalia's fledgling army as well as carrying out its own operations against the Shabaab and a separate self-proclaimed Islamic State group in the north of the country -- has increased the frequency of air strikes targeting militant leaders.