According to the study, by the year 2050 there could be some 1.2 billion underage girls forced into child marriage.
A new report using UN statistics estimates there are about 700 million girls around the world who were forced to get married before the age of 18.
The Save the Children report -- issued on October 11 to mark International Day Of The Girl Child -- said a girl under 15 is forced into marriage every seven seconds and that many girls only 10 years of age are being forced to marry.
Citing statistics from the UN children's agency UNICEF, the study says that by the year 2050 there could be some 1.2 billion underage girls forced into child marriage.
The report, titled Every Last Girl, says early marriage for girls usually prevents them from getting an education, from seeking work, and often continues a cycle of poverty.
"Early marriage starts a cycle of disadvantage that denies girls the most basic rights to learn, develop, and be children," said Susanna Krueger, CEO of Save the Children Germany, in a statement.
The study ranks 144 countries on its treatment of girls.
Afghanistan was 121st on the list, and Pakistan was 88th. Iran (70th), Azerbaijan (69th), Georgia (62nd), Kyrgyzstan (59th), and Tajikistan (57th) were also rather low in the rankings.
Serbia (20th), Belarus (24th), Macedonia (28th), and Kazakhstan (30th) placed high on the list.
Countries in Sub-Saharan Africa have the worst record for the mistreatment of girls, but the United States and Britain also have a disproportionately high rate of teenage pregnancies and child marriages were deemed to be "relatively common" in Germany.
With reporting by dpa
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