As a UN-sponsored conference on the humanitarian crisis in the Lake Chad basin opens in Berlin, one rights group has highlighted the plight of teenage girls.

Plan International says adolescent girls in an area, which includes parts of Nigeria, Niger, Chad and Cameroon, face violence from both Boko Haram insurgents and their own communities.

The organisation says the teenagers are vulnerable to kidnap, rape and forced marriage, while rape victims often end up as prostitutes after being rejected by their own families.

Relief agencies say 11 million people need humanitarian assistance in the region due to a nine-year conflict.