* Militant group gives 7-day notice of attack
* Bomb blasts and fallout highly politicised
(Adds details, background)
By Nick Tattersall
LAGOS, Oct 15 (Reuters) - A Nigerian militant group said on Friday it planned to carry out another bomb attack in the capital Abuja this month, after claiming twin car bombs in the city two weeks ago which killed at least 10 people.
The Oct. 1 blasts near an independence day parade and the threat of further violence have raised political tensions in Africa's most populous country as it prepares for nationwide elections due to be held next April. [ID:nLDE69E21E]
The Movement for the Emancipation of the Niger Delta (MEND) said it was giving the government "about seven days' notice" ahead of the next attack, which it said would be in response to the handling of the independence day bombs.
It accused President Goodluck Jonathan's administration of arresting innocent people following the Oct. 1 attacks and said Henry Okah, a militant leader on trial in South Africa over the bombings, was innocent.
The presidency has said the investigations are based on U.S. and British as well as Nigerian intelligence.
"Since both (the Nigerian and South African) governments are bent on blaming innocent persons on ridiculous insinuations and unrelated evidence, we have decided to carry out another attack in Abuja without altering our mode of operation to prove the suspects' innocence," the emailed statement said.
"As usual we will give a 30 minutes advance warning to avoid civilian casualties, then sit back and watch how the blame game will be played out on all those already falsely accused."
The warning was sent from the same Yahoo! email address and signed with the same pseudonym, Jomo Gbomo, used by MEND to claim both the independence day bombings and previous attacks on oil infrastructure in the Niger Delta.
In a follow-up email to Reuters, Gbomo said "we are giving the government about seven days' notice to put every security measure they have in place before we strike".
MEND issued a similar statement warning of imminent attacks around an hour before two car bombs went off in Abuja on Oct. 1.
Nigeria is a generally peaceful country of more than 200 ethnic groups, but regional rivalries and tribalism bubble under the surface and the bombings and subsequent response by the authorities have become highly politicised.
Jonathan, a southerner, already faced a tough battle convincing some in the ruling party to back his bid for the upcoming elections and to jettison a gentleman's agreement that means the next president should be a northerner.
The unwritten pact in the People's Democratic Party is meant to ensure the balance of power by rotating the presidency every two terms between north and south. [ID:nLDE68H047]
Jonathan is the first head of state from the Niger Delta, home to the country's oil industry, and brokered an amnesty with rebels including most of MEND's field commanders last year.
The group's claim of responsibility was an embarrassment for Jonathan, who said its name had been used as a cover and that the attacks had nothing to do with the Niger Delta.
His northern rivals seized on the comments to accuse him of partisanship, particularly after the campaign manager for his main northern challenger, former military ruler Ibrahim Babangida, was detained for questioning.
Jonathan's camp accused them of "ethnic chauvinism".
The violence bodes ill for polls set to be the most fiercely contested since the end of military rule just over a decade ago.
"An exchange of accusations by politicians from opposing camps about the source of the violence (on Oct. 1) has exacerbated an already volatile situation," U.S.-based election watchdog the National Democratic Institute (NDI) said.
"Some citizens ... expressed fears that a "do or die" mentality could heighten negative competition and raise the risk of politically motivated violence," it said after a five-day assessment of the country's election preparations. (For more Reuters Africa coverage and to have your say on the top issues, visit: http://af.reuters.com/ ) (Editing by Jon Boyle)
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