Human Rights Watch urged Yemen's government on Thursday to ban marriages of girls under the age of 18, warning it deprives child brides - often forced to wed much older men - of education and harms their health.

The New York-based group said the political paralysis born of 10 months of protests aimed at ousting President Ali Abdullah Saleh had drawn attention away from the phenomenon of child marriage, but that Yemen's government must address it.

Girls should not be forced to be wives and mothers, Nadya Khalife, the author of a 54-page report entitled: How Come You Allow Little Girls to Get Married?, said in a statement.

The government...needs to show that it has the political will to do this by adopting this law, she told Reuters, calling for a law to set 18 as the minimum age for marriage.

As Yemen undergoes political change, leaders should seize the opportunity to correct an injustice that does enormous harm and set the country on a new course of social justice, including equality for women and girls, Khalife's statement said.

Saleh last month signed a deal brokered by Yemen's richer Gulf neighbours aimed at averting civil war. It stipulates he formally renounce his powers, and that an interim government lead the country to a presidential vote in February.

Quoting United Nations and government data, HRW said nearly 14 percent of Yemeni girls were married before the age of 15 and 52 percent before the age of 18. The group says many Yemeni child-brides-to-be are kept from school when they reach puberty.

The report also said bearing children at a young age caused lasting reproductive health problems.

In 2009, a group of conservative Yemeni lawmakers blocked legislation setting the minimum age for marriage at 17, arguing the bill contradicted Islamic law.

Child marriage in Yemen drew international attention last year, when a 13-year-old Yemeni girl died from internal bleeding after intercourse with a spouse twice her age, and a Yemeni girl published a translated account of her marriage at age 9 to a man three times her age.

(Reporting by Mahmoud Habboush; Editing by Michael Roddy)