The military's Africa Command said the strike occurred at about 1:30 am local time some 300 miles southwest of Mogadishu.
"Working from actionable intelligence, the Department of Defense conducted a successful collective self-defense strike operation against an al-Shabaab troop concentration," Africom said in a statement.
It was the third US strike on Shabaab Islamist militants since President Donald Trump authorized the Pentagon in March to take counter-terrorism actions -- whether airstrikes or ground raids -- when it deems them necessary to support the Somali government.
It was within the Pentagon's "parameters of authority to engage in collective self-defense of our Somali partners," Pentagon spokesman Navy Captain Jeff Davis said.
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Before Trump broadened the Pentagon's authorities, US military actions in the eastern African country each required high-level review by different agencies.
US special forces have been deployed in Somalia for years. There are currently about 50 US troops there.
Shabaab, an Al-Qaeda linked group, has been fighting since 2007 to overthrow the internationally backed government in Somalia.