It follows another video in July that the rights group said showed Cameroonian forces shooting two women with small children strapped to their backs as suspected Boko Haram extremists.
The growing concerns about alleged abuses by a U.S. security ally pose a challenge to 85-year-old President Paul Biya, one of Africa's longest-serving leaders, who is running for another term in October after taking office in 1982.
Cameroonian authorities have arrested seven soldiers suspected to have committed the acts reported Friday by Amnesty International, said government spokesman Issa Tchiroma Bakary, who called the crimes unacceptable.
Biya has ordered investigations into the shootings and many more people may be arrested in the days ahead, Bakary said.
In the past the government has denied such killings by security forces as they combat Boko Haram, whose fighters have spilled over the border from Nigeria and carried out bombings and other attacks. The government has said reported abuses are investigated and defended the professionalism of its troops.
The latest video shows soldiers firing automatic weapons at people lying down and cowering against a wall while buildings burn in the background in the village of Achigaya. One soldier approaches, looks over the bodies and fires again at close range. Then the soldiers walk away.
Amnesty International said its analysis shows the video was apparently made by soldiers and was likely recorded before May 2016. The rights group said its analysis of weapons, dialogue and uniforms determined that the shooters were Cameroonian forces.
"Speaking in French, the soldiers describe themselves as carrying out a 'kamikaze' operation," the rights group said.
It said the video backed up its July 2016 report that documented the killings of more than 30 people, including several elderly people, in the same village after a military operation that tried to recover the bodies of soldiers killed in Boko Haram.
Cameroon has sought to dismiss the earlier video showing women and children, with its ambassador to Canada this week telling reporters in Washington: "You know what Photoshop can do."
Anna reported from Johannesburg.
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