Donor nations, led by the US, point to the Elimination of Violence Against Women (EVAW) law as a prized symbol of the success of the international effort in Afghanistan since 2001.
But a report released by the UN said that prosecutions and convictions remained low under the 2009 law, which criminalises child marriage, forced marriage, forced self-immolation, rape and other violence against women.
"Implementation has been slow and uneven, with police still reluctant to enforce the legal prohibition against violence," Navi Pillay, the UN High Commissioner for Human Rights, said.
"Afghan authorities need to do much more to build on the gains made so far in protecting women and girls."
The report comes amid fears that as the NATO-led military mission prepares to withdraw by the end of next year, religious conservatives are seeking to increase their influence and undermine advances in women's rights.
The report said that of about 1,670 registered incidents of violence against women in 16 provinces, only 109 cases - seven percent - went through a judicial process using the EVAW law.
Many cases were resolved through informal mediation, which often fails to protect women from further violence, the United Nations Assistance Mission in Afghanistan (UNAMA) said.
One 24-year-old witness from Nangarhar province told UN researchers how she was forced into a marriage when she was 15.
"He regularly subjected me to violence including beating and abuse," she said.
"My husband gave a written statement to the police that he would refrain from violence and I went back with him.
"Within a month he started beating me again. He tried to kill me when neighbours intervened to save me.
"My case has been mediated three times by local elders, shuras, jirgas and the Department of Women's Affairs. My family does not want me to do anything legal. I have suffered a lot and I want justice."
The report also said the Supreme Court had convicted 283 people, mostly women, of "attempted zina (sexual intercourse outside of marriage)" in a one-year period to March 2013.
During the 1996-2001 Taliban era, girls were banned from school, and women were forced to wear burqas and not allowed to take part in any form of public activity.
"Increases in reporting and registration of incidents of violence against women by Afghan authorities are encouraging," said UNAMA head Jan Kubis.
"But it is a real concern that these positive steps have not been met with increased use of the EVAW law to indict and prosecute those who commit violence.
"Until the EVAW law is enforced fully, progress in ending violence against women and advancing women's rights in Afghanistan will be limited."
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