By Tife Owolabi
YENAGOA, Nigeria (Reuters) - More than 1,800 prisoners are on the run in southeast Nigeria after escaping when heavily armed gunmen attacked their prison using explosives and rocket-propelled grenades, the authorities said on Tuesday.
Nigerian police said it believed a banned separatist group, the Indigenous People of Biafra (IPOB), was behind the attack in the city of Owerri, but a spokesman for the group denied involvement.
The secessionist movement in the southeast is one of several serious security challenges facing President Muhammadu Buhari, including a decade-long Islamist insurgency in the northeast, a spate of school kidnappings in the northwest and piracy in the Gulf of Guinea.
"The Owerri Custodial Centre in Imo state has been attacked by unknown gunmen and forcefully released a total of 1,844 inmates in custody," a Nigerian Correctional Service spokesman said in a statement late on Monday. The attackers stormed the facility at around 2:15 a.m. (0115 GMT) on Monday, he said.
The police said attackers used explosives to blast the administrative block of the prison and entered the prison yard.
"Preliminary investigations have revealed that the attackers... are members of the proscribed Indigenous People of Biafra (IPOB)," said Frank Mba, a spokesman for the Nigeria Police Force.
IPOB wants independence for a region in southeast Nigeria it calls Biafra. One million people died in a 1967-70 civil war between the Nigerian government and secessionists in Biafra.
Tensions have increased in the southeast in recent months in the wake of accusations that a paramilitary wing of IPOB, known as the Eastern Security Network (ESN), has been involved in clashes with the military.
But an IPOB spokesman told Reuters the group did not carry out the prison attack.
"IPOB and ESN were not involved in the attack in Owerri, Imo state. It is not our mandate to attack security personnel or prison facilities," the IPOB spokesman said in a phone call.
Several police stations have been attacked in southeastern Nigeria since January, with large amounts of ammunition stolen. No groups have claimed responsibility for the attacks.