Boko Haram have abducted huge numbers of women and children. (File)

Tens of thousands of women have been freed from Nigeria's brutal Boko Haram fighters, but providing a safe future for them is critical to winning the war, analysts warned Tuesday.

"Their hardship is a humanitarian concern - but also could fuel the conflict," the International Crisis Group (ICG) said in a new report.

Boko Haram's decade-long uprising to establish a hardline ISIS in Nigeria's northeast has spilt into neighbouring Niger, Chad and Cameroon.

A regional military coalition is battling the Islamist group.

But success cannot depend on the armed forces alone, the ICG warned.

They called on the government to "look beyond the military campaign", in a report released on Tuesday, entitled "Returning from the Land of Jihad: The Fate of Women Associated with Boko Haram."

Those who have escaped the group are often now living among the same communities badly hit by violence, ICG said.

Many women fleeing the jihadists are shunned by society and find it hard to marry -- leaving them vulnerable to assault, the report read.

"The successful reintegration of former Boko Haram women can send a powerful signal to their fighter husbands, some of whom are eyeing the possibility of their own surrender," the ICG said.

"Conversely, their mistreatment could not only dissuade men from demobilising but also prompt women to return to the insurgents' ranks."

'Litmus test'

That applies to both those who were forcibly made to fight because they were abducted, and those who were recruited willingly, but have since broken away from the group and surrendered.

ICG said how the women were treated provided a "litmus test" for those still fighting.

"If returnee women report fair treatment, they may convince disillusioned insurgents to leave Boko Haram's ranks," ICG said.

They called for greater funding to support programmes for the women, as well as ensuring that aid is distributed equally, to avoid building up resentment towards the ex-fighters from those who suffered from Boko Haram attacks.

"Increasing support for people displaced by the conflict, and more generally for the north east's development, can help repair the frayed relations between state and society... that have fuelled the insurgency," the report said.

Boko Haram have abducted huge numbers of women and children -- including the kidnapping of 276 girls from a school in Chibok in 2014 that grabbed media attention -- but they are not the only ones holding women and children.

Earlier in May a pro-government militia force fighting Boko Haram released 894 children, including 106 girls.

Fighting continues.