Lagos - UN Secretary-General Ban Ki-moon on Friday called on Nigeria to step up medical and psychological aid to survivors of Boko Haram attacks and victims of rape.
Nigeria's military, backed by its neighbors, has liberated a series of towns from Boko Haram control in an operation launched in February.
Women and girls have since come forward with testimony of horrific rape and sexual violence while residents have given accounts of children being used as suicide bombers.
Ban said he was "appalled" by the victims' accounts and called on "the government of Nigeria to scale up the provision of medical and psychosocial support to the survivors."
International Committee of the Red Cross president Peter Maurer on Thursday described Boko Haram violence as "one of the most serious humanitarian crises in Africa" and called for additional funding to help victims.
"Whole communities have fled their villages and endured unimaginable suffering...They need support far beyond what the ICRC can provide, yet in many hard-hit places we find ourselves alone," said Maurer after a visit to affected regions.
The United Nations has criticized Nigeria's handling of the Boko Haram crisis, noting that the military had been slow to respond to the violence.