Guatemala has raised the minimum age for marriage to 18, but women's rights campaigners said enforcing the new law would be a challenge in a country where nearly one-third of girls are currently married by that age.
The law, approved by Congress earlier this month by 87 votes to 15, raised the minimum marriage age from 14 for girls and 16 for boys, but said 16-year-old girls would still be able to marry with a judge's permission under some circumstances.
Christa Stewart, of women's rights charity Equality Now, hailed the law as "a really important step in recognizing the full potential of girls and reframing how girls should be treated in society."
"It requires a cultural shift to fully implement the law, the training of judges, and reaching remote rural areas," Stewart told the Thomson Reuters Foundation in a telephone interview.
Rights campaigners say achieving the cultural change the law envisages will be a particular challenge for Guatemala's Maya indigenous communities, who live in poor rural areas where child marriage is most common.
The U.N. children's agency (UNICEF) says seven percent of Guatemalan girls are married by the age of 15 and 30 percent by 18.
A quarter of Guatemalan births are to teenage mothers - one of the highest rates in Latin America - and campaigners hope the ban on child marriage will help prevent teenage pregnancy and stop girls dropping out of school.
"If a girl is married, there is the presumption there will be child bearing and they are more likely not to continue with their education," Stewart said.
Most Latin American countries ban marriage until 18, and many of them allow children to get married at a younger age with the permission of parents or a judge.
Complications in pregnancy and childbirth are the second highest cause of death for 15- to 19-year-old girls globally, and babies born to adolescent mothers face a 'substantially higher risk' of dying than those born to women in their early 20s, according to the World Health Organization.
Child marriage, often to a much older man, deprives girls of education and opportunities, keeping them in poverty, and put them at greater risk of domestic and sexual violence, rights groups say.
Each year more than 15 million girls worldwide are married before they turn 18, according to campaign group Girls not Brides.
Ending child marriage by 2030 is among the targets set out in the U.N. Sustainable Development Goals recently adopted by world leaders.