The US military conducted an airstrike against a group of Shabaab militants in Somalia early Wednesday, officials said, the third such action in a month.

The military's Africa Command said the strike occurred at about 1:30 am local time some 480 kilometers southwest of Mogadishu.

"Working from actionable intelligence, the Department of Defense conducted a successful collective self-defence 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 authorised the Pentagon in March to take counter-terrorism actions -whether airstrikes or ground raids — when it deems them necessary to support the Somali government.

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Self-defense

Wednesday's strike follows a July 2 attack on Shabaab militants and a June 11 raid of a training centre.

It was within the Pentagon's "parameters of authority to engage in collective self-defence of our Somali partners," Pentagon spokesman Navy Captain Jeff Davis said.

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.

READ: US drone strikes Shabaab base in Mogadishu

Shabaab, an Al-Qaeda linked group, has been fighting since 2007 to overthrow the internationally backed government in Somalia.