LAGOS (Reuters) - Nigeria's electoral commission on Friday suspended voter registration in most parts of oil-producing Imo state after an election official was shot dead by unknown gunmen, as the country prepares for a series of votes early next year.

       Armed groups have since last year burned down electoral offices and police stations in states in the southeast, which government blames on the banned separatist Indigenous People of Biafra (IPOB) group. IPOB denies the charges.

       Independent Electoral Commission of Nigeria spokesman Festus Okoye said in a statement voter registration had been suspended at 54 centres and in three local government areas in Imo state, following the attack on Thursday.

       Voter registration is taking place across Nigeria ahead of elections due next year that will choose a new parliament and president in February - with Muhammadu Buhari stepping down after serving the two consecutive four-year terms allowed by the constitution - and state governors in March.

       But the country is plagued by growing insecurity, seen in gun attacks and kidnappings in the northwest, a festering Islamist insurgency in the northeast and attacks on government institutions by armed groups in the southeast.

       Separatist groups like IPOB campaign for southeastern Nigeria, homeland of the Igbo ethnic group, to be an independent country. The region attempted to secede in 1967 under the name Republic of Biafra, triggering a three-year civil war in which more than a million people died, mostly of starvation.

       (Reporting by MacDonald Dzirutwe; Editing by Alison Williams)