(CNN)Nearly 2000 inmates broke free from a prison in southeast Nigeria Monday after armed men invaded the site and used explosives to blast parts of the prison, authorities said.
Six of the 1,844 inmates who escaped from the Owerri Custodial Centre, Imo State, have voluntarily returned, according to a spokesman for the Nigerian Correctional Service.
Thirty-five others chose not to abscond during the attack, authorities said.
"The attackers who stormed the facility at about 0215hrs on Monday 5th April, 2021, gained entrance into the yard by using explosives to blast the administrative block," said Francis Enobore, spokesman to Nigerian prison service.
The Nigeria Police Force has blamed outlawed secessionist group, the Indigenous People of Biafra (IPOB) and its paramilitary wing, the Eastern Security Network (ESN) for the attack.
The police said the gunmen, who had also stormed the Force headquarters in the state, were armed with a variety of sophisticated weaponry and military hardware.
"The attempt by the attackers to gain access to the Police armoury at the Headquarters was totally and appropriately resisted by Nigeria Police Force," the force said in a statement Monday, adding that no lives were lost in the incident.