Cultural traditions and a lack of legal protections are driving tens of millions of girls around the world into early marriage, subjecting them to violence, poverty and mistreatment, an international human-rights group has said.

Equality Now, citing the United Nations Population Fund, said in a report issued over the weekend that more than 140 million girls over the next decade will be married before they turn 18.

"When a young girl is married and gives birth, the vicious cycle of poverty, poor health, curtailed education, violence, instability, disregard for rule of law ... continues into the next generation, especially for any daughters she may have," the report said.

The 32-page report found that despite laws that set a minimum age for marriage in many countries, social norms continue to provide a veneer of legitimacy to child marriage in remote villages and even in developed countries. Child marriage is defined as a marriage before age 18.

"Child marriage legitimizes human-rights violations and abuses of girls under the guise of culture, honor, tradition and religion," the report said.

The report gave examples of cases in countries such as Afghanistan, Cameroon, Guatemala, India, Jordan, Kenya, Malawi and Mali.

Often when child brides are married off to older men, it is to restore or maintain family honor or to settle a father's debts or obtain some other financial gain. A girl married off is seen as one less mouth to feed, and her family members often spend the dowry to support themselves.

In some countries, families encourage early marriage to protect young girls from premarital sex and to uphold a family's honor, according to the report.

In one case, the report recounts what happened to Mariam, a girl who was born in France to parents from Mali. She had never been to Mali until she was 14, and she visited with her sister, who was 16.

When they arrived, their father took their passports, and Mariam was told to marry her father's cousin. Her sister was to marry the local imam. Mariam eventually escaped with the help of a policeman she met during a visit to the village market, but her sister remains in Mali, the report said.