More than 1,800 inmates escaped from a Nigeria prison after an attack by gunmen carrying rocket-propelled grenades, machine guns, explosives and rifles, the BBC reported on Tuesday.

The attackers used explosives to blast the administrative block of the prison in the southeastern town of Owerri and enter the prison yard, the BBC said. Owerri is about 400km southeast of Nigeria’s largest city, Lagos.

The Nigerian Correctional Service confirmed to BBC that 1,844 inmates escaped after the attack early on Monday. Nigerian police blamed the attack on the banned separatist group, the Indigenous People of Biafra, the BBC said.