Gunmen bombed the headquarters of the electoral commission in Nigeria's southeastern Imo state on Monday and killed a policeman during a gunfight, police spokesman Michael Abattam said.
Elections have in the past been marred by violence in Nigeria, which holds a presidential vote in February to elect a successor to President Muhammadu Buhari, now in his second and final term.
Imo is one of the states in the southeast where gunmen have attacked electoral officials, killed politicians and security agents this year. The government blames the separatist group Indigenous People of Biafra, which has denied the charge.
Abattam said the Independent National Electoral Commission (INEC) office in the state capital Owerri was attacked at about 3 a.m. (0200 GMT).
"They threw bombs on the roof of the INEC building but unfortunately for them, they were resisted by our men who were guarding the place," Abattam said.
He said the police repelled the attack after receiving reinforcements.
"Fortunately, we neutralised three of them. Others escaped with bullet wound injuries," he said, adding that a policeman was killed and another injured.
Two other gunmen were arrested and police recovered explosives, phones and five rifles.
INEC said in a statement no critical election materials were damaged. It added that this was the third attack on its facilities in Imo state this month.
By Anamesere Igboeroteonwu, Reuters
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