Amnesty said its investigations revealed the trio killed in the March 18 strike in southern Somalia were innocent, despite US Africa Command (AFRICOM) saying the men were jihadists.

The US has stepped up drone strikes in Somalia in 2019 against what it says are fighters from Al-Shabaab, a militant outfit linked to Al-Qaeda, and the Islamic State in Somalia.

But Amnesty alleges civilians have been among the dead, claiming it has documented more than a dozen cases of innocent people being killed in US air raids.

The international rights group said AFRICOM had provided no evidence to support its assessment the three men were militants.

It also accused the US military of failing to follow up claims the men were innocent despite promising to do so, or make any effort to contact their families.

"It's bad enough that the US Africa Command appears not to know who its air strikes are actually killing and maiming in its secretive war in Somalia," Abdullahi Hassan, a Somalia researcher for Amnesty, said in a statement.

"But it's reprehensible that AFRICOM offers no way for those affected to contact it and has failed to reach out to the families of victims after its version of events was called into question in this case."

Amnesty says it interviewed 11 people about the March 18 strike, including co-workers and family of the men killed when their car was hit in Lower Shabelle, a hotbed of the Islamist insurgency in southern Somalia.

It said all those interviewed in the investigation "were adamant that none of the men was a member of Al-Shabaab".

In a March 19 press release confirming the strike, AFRICOM said "it assessed this air strike killed three (3) terrorists" and it was aware of reports of civilian casualties.

AFRICOM spokesman John Manley told AFP that "as explained to Amnesty International, based on detailed methods and a body of multi-intelligence reporting, to include the actions observed from the vehicle, U.S. Africa Command arrived at reasonable certainty the vehicle and its occupants were al-Shabaab and actively supporting al-Shabaab operational activity."

"U.S. Africa Command minimizes the risk to civilians by following a thorough, reasonable methodology that accounts for weapons effects and mitigates risk to civilians."

US strikes in Somalia surged in April 2017 after President Donald Trump declared the south of the country an "area of active hostilities". The rate of air strikes rose sharply in 2019.

Al-Shabaab have been waging an insurgency against Somalia's foreign-backed government for over a decade, and while it has lost ground, continues to stage deadly attacks.

On Monday, militants attacked an EU convoy in Mogadishu and Baledogle, a US military base northwest of the capital from where drone operations are launched.