Gambia has banned child marriages with immediate effect as husbands and parents of any girl who is wed will face 20 years in prison.

But President Yahya Jammeh was warned the decision could spark a backlash in a country where a third of girls get married before they turn 18.

People who were aware of child marriage yet chose not to report it could face a sentence of 10 years, Jammeh added.

Christa Stewart of the London-based women’s rights organisation Equality Now said: ‘We hope that a law will be enacted immediately and that strong action will follow to ensure that every single girl is protected.’

Almost a third of women aged between 20 and 24 in Gambia were married before the age of 18, and nearly a tenth before 15, according to data from the U.N. children’s agency (UNICEF).