The United Nations children's agency accused Yemen's Al-Qaeda affiliate of sexually exploiting children, pointing to incidents in the south in 2012 in a report published Tuesday.
Al-Qaeda loyalists forced around 100 girls, some as young as 13, to marry its fighters in the southern province of Abyan in 2012, UNICEF said.
Taking advantage of a collapse of central authority during a 2011 uprising that forced veteran strongman Ali Abdullah Saleh from power, Al-Qaeda seized large swathes of the south and east.
Al-Qaeda fighters seized swathes of Abyan province, east of the main southern city of Aden, in 2012.
Both girls and boys had been "exposed to sexual violence in conflict situations in Yemen," the report said.
"One of the forms of this violence is the forced marriage of up to 100 girls in the province of Abyan, attended by the heads and fighters of Ansar al-Sharia," the UN agency said, using a front name adopted by Al-Qaeda loyalists.
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"Seven cases of forced marriage involving girls under 13 have been verified," UNICEF said.
In addition to that, "two girls were given as a gift" to members of the network by their brothers who had just joined the organisation.
In other cases, fighters paid dowries of up to $5,000 (3,700 euros) to marry the daughters of families from the region, some of which earn little more than $12 per month, UNICEF said.
Most of the girls married off to Al-Qaeda fighters were abandoned by their husbands when the army retook the area in June 2012, the report said.
Some of them had given birth, the report added.
UNICEF said it was more difficult to document the sexual abuse of young boys recruited by the jihadists, but that it had recorded three cases in 2012.
Washington regards the Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP) as the network's deadliest affiliate and has stepped up drone strikes targeting its leaders.