The U.N. children's agency says a 12-year-old girl who says she was raped by a U.N. peacekeeper in Central African Republic went through "a most brutal ordeal," and the United Nations is pledging to fully investigate all allegations of sexual misconduct and hold perpetrators accountable.

Amnesty International last week accused peacekeepers of the rape, and of the indiscriminate killing of a 16-year-old boy and his father, in separate incidents Aug. 2 and Aug. 3.

Secretary-General Ban Ki-moon then fired the head of the peacekeeping mission in Central African Republic, an unprecedented action.

Vannina Maestracci, a spokeswoman for Ban, said Monday that U.N. investigations are "complicated by the large number of nationalities of police and military personnel" involved in the operation where the alleged attacks occurred.