At least 15 million teenage girls worldwide have been forced into sex — often by partners, relatives or friends — yet only 1 in 100 sought help, the United Nations said on Wednesday.

Cameroon had the highest rate of sexual violence, with 1 in 6 teenage girls experiencing forced sex, the U.N.'s children's agency (UNICEF) said in a report which examined data from more than 40 countries.

"This idea of women being at the disposal of men is a big factor driving the experience of sexual violence of girls," said report author Claudia Cappa.