Humanitarian agencies fear the central African nation of Cameroon is on the brink of civil war.
Around 18,000 people have been forced to flee their homes in the west of the country, where government forces and minority English-speaking separatists are locked in a vicious conflict.
Video shows armed men, in what appear to be military uniforms of the Commonwealth country, carrying out the shootings of women and their children.
The incident is said to have happened in the north of Cameroon, near the Nigerian border. As part of the drive to eradicate Boko Haram, Britain and the US have helped train the Cameroon Army.
The Cameroon government told has said the atrocity does not involve its soldiers and the video could be fake.