The Somalian parliament is considering a bill that would allow child marriage once a girl's sexual organs mature.
The new Sexual Intercourse Related Crimes Bill would allow forced marriage as long as the family gives their consent.
It marks a dramatic reworking of years of efforts give more protections to women in one of the world's most conservative countries.
The bill 'would represent a major setback in the fight against sexual violence in Somalia and across the globe', said the United Nations special representative on sexual violence in conflict.
Pramila Patten said it should be withdrawn 'immediately' in a statement on Tuesday, adding it also weakens protections for victims of sexual violence.
Already more than 45 per cent of young women in Somalia were married or 'in union' before age 18, according to a United Nations analysis in 2014-15.
Somalia in 2013 agreed with the U.N. to improve its sexual violence laws, and after five years of work a sexual offences bill was approved by the Council of Ministers and sent to parliament.
But last year the speaker of the House of the People sent the bill back 'in a process that may have deviated from established law' asking for 'substantive amendments,' the U.N. special representative said.
The new bill 'risks legitimising child marriage, among other alarming practices, and must be prevented from passing into law,' U.N. human rights chief Michelle Bachelet said this week.
She warned that its passage would 'send a worrying signal to other states in the region.'
Thousands of people in Somalia are circulating a petition against the bill, including Ilwad Elman with the Mogadishu-based Elman Peace organization.
As Somalia prepared to mark International Youth Day on Wednesday, Elman tweeted this week: 'I don't wanna see any Somali officials participating online to celebrate ... when you're trying to steal their childhood away from them RIGHT NOW with the intercourse bill legalizing child marriage.'
The U.N. mission to Somalia in a separate statement has called the new bill 'deeply flawed' and urged parliament to re-introduce the original one.
That original bill 'will be vital in preventing and criminalizing all sexual offenses,' the Somalia representative for the U.N. Population Fund, Anders Thomsen, said.
'Big moment for MPs to decide Somalia´s future values,' the British ambassador to Somalia, Ben Fender, has tweeted.
The contentious new bill comes as women's rights groups openly worry that the coronavirus pandemic and related travel restrictions in Somalia have worsened violence against women and female genital mutilation.
Nearly all Somali women and girls have been subjected to that practice.
Some 68 per cent of more than 300 service providers across the country have reported an increase in gender-based violence, including rape, since the pandemic began, UNFPA said in a report last month.
Nearly a third of respondents, including more than 750 community members, said they believed child marriages had increased in part because of economic pressures and in part because schools have been disrupted.
And in some cases, health facilities have closed, limiting access to care.
It comes as, severe flooding continues to displace thousands of people in Somalia.
The government in recent days issued new warnings to communities living along the Jubba and Shabelle rivers.
It said rains in the highlands of neighbouring Ethiopia could lead to flash floods in towns such as Jowhar and Beledweyne.
Residents have said several people have been swept away.
The United Nations has said at least four displaced people have died. More than 100,000 people have had to flee their homes since late June.
President Mohamed Abdullahi Mohamed has appealed for emergency relief for Afgoye town outside the capital, Mogadishu.
Afgoye has seen some of the worst flooding, with parts of town swept away and thousands of families left without power.
© Associated Newspapers Ltd.