UNHCR spokesman Babar Baloch told a regular UN briefing in Geneva that the residents panicked and fled after the Multinational Joint Task Force, which had gone to secure Rann, left the city.
Refugees said Boko Haram subsequently promised to return to Rann, Baloch said, according to Reuters.
Boko Haram is an extremist group responsible for dozens of massacres of civilians and the abduction of people, especially women and girls in Nigeria and neighboring countries.
The group’s militancy is estimated to have killed more than 27,000 people and forced 1.8 million others to flee their homes, also triggering a humanitarian crisis in Nigeria.