The release of a video purporting to show some of the Nigerian Chibok schoolgirls kidnapped by Boko Haram apparently happy with their lives is a propaganda strike to show the Islamist group is unbowed, security experts said on Monday.

The video shows a group of about 12 teenage girls and young women, some of them holding babies.

"We are the Chibok girls. We are the ones you are crying about for us to come back. By the grace of Allah, we are never coming back," said one of the girls in the Hausa language widely spoken in northern Nigeria.