Despite gains in some countries, more than 14 million girls under age 18 will be married each year over the next 10 years, a figure expected to increase to more than 15 million girls a year between 2021 and 2030, according to a new report from the U.N. Population Fund (UNFPA) released on Thursday.

As the number of girls who are married as children grows, the number of children bearing children will increase, and deaths among girls will rise, said the report, timed to mark the inaugural International Day of the Girl Child.

International conventions declare that child marriage is a violation of fundamental human rights because it denies girls the right to choose when and with whom to marry.

The negative implications are far-reaching for girls, often leading to their early departure from school, economic dependency and difficulty finding a vocation or work outside the home. The practice can also perpetuate cyclical poverty and increase susceptibility to such sexually transmitted diseases as HIV/AIDS.

"In those communities where the practice of child marriage remains common, families can feel it’s not worth investing at all in the education of their daughters,” said Babatunde Osotimehin, UNFPA’s executive director who last month launched a global campaign urging countries to invest in the education of women and young people.