The accusation relates to an incident on January 10 that the army, which is fighting armed separatists in the region, says was a fight with "terrorists."

"Witnesses said that over 50 soldiers... entered Mautu on foot at about 2 pm on January 10 and started shooting indiscriminately as people fled," HRW said.

"The witnesses said that soldiers killed nine people, including a 50-year-old woman and a six-year-old girl, and went house-to-house searching for separatist fighters and weapons, threatening residents and looting people's belongings," it said in a statement.

The same day, several videos and photos were posted on social media including one showing a woman and child clearly being shot dead. Another showed several men lying on the ground.

HRW said the footage "matched the victims filmed with the descriptions of the victims known to have been killed" and concluded "that the videos were captured within hours of the attack."

On January 11 the army denied killing any civilians at Mautu, saying it had carried out a "preventive" raid on "terrorist groups' positions."

"Armed individuals... immediately opened fire" on the soldiers, who "inflicted an appropriate response on them," army spokesman Cyrille Serge Atonfack Guemo said, adding that the army acted in "strict respect of the rules of engagement".

"Several terrorists were neutralised, others were wounded or put to flight," he said.

Results of a "detailed investigation" promised by the army have yet to be made public.

France, the influential former colonial power, on January 12 issued a statement to "condemn the attack" at Mautu, which it said had claimed the lives of eight civilians. It did not apportion blame.

Mautu lies in the Southwest Region, which with the neighbouring Northwest Region is home to Cameroon's English-speaking minority.

In 2017, resentment over years of perceived discrimination at the hands of the francophone majority resulted in a declaration of independence by anglophone radicals.

Their self-declared state, Ambazonia, has not been recognised internationally, and the central government in Yaounde has responded with a crackdown.

Civilians are often caught up in the fighting, suffering at the hands of both sides, international aid groups and the UN say.

So far more than 3,000 people have died and more than 700,000 have fled their homes during the conflict.

On December 17, a trial opened in Yaounde of three soldiers accused of kiling 13 civilians in the village of Ngarbuh, in the Northwest Region, in February 2020.

The government initially dismissed any responsibility for civilian deaths.

It blamed fatalities on an "unfortunate accident" that occurred when a fuel tank exploded in a fire fight between soldiers and "terrorists."

The UN says 23 civilians were killed in that incident, including 15 children and two pregnant women.