ABUJA (Reuters) - Nigeria's multiple security problems have created a crisis that requires urgent attention and could lead to instability in other African countries if it is not addressed, a United Nations rapporteur said on Monday.

Security forces in Africa's most populous country are trying to tackle a decade-long Islamist insurgency in the northeast, banditry in the northwest and bloody clashes between nomadic herdsmen and farming communities over dwindling arable land in central states.