* Death toll from car bombs climbs to 12, with 17 injured
* Security service admits it was tipped off
* Rebel group says attack is not start of new campaign
(Updates with quotes from rebel group, president)
By Camillus Eboh
ABUJA, Oct 2 (Reuters) - The death toll from car bombs that exploded near a parade marking Nigeria's 50th anniversary of independence rose to 12 on Saturday and authorities admitted they had been warned of the attack.
Jimoh Moshoo, police spokesman in the capital, Abuja, said 17 people were wounded in Friday's blasts, which went off about an hour after an emailed bomb threat from a rebel group in the oil-producing Niger Delta.
The Nigerian newspaper This Day, citing presidency sources, said British intelligence had got wind of a plot and passed on a warning to Abuja. Britain's Duke of Gloucester, who was due to represent Queen Elizabeth at the event, pulled out.
The secret service in Africa's most populous country confirmed it had received foreign tip-offs and had stepped up security accordingly, including towing 65 vehicles from the streets and cordoning off roads leading to the parade ground.
"If we had ignored them the situation could have perhaps been worse than what happened," State Security Service spokeswoman Marilyn Ogar said.
News organisations including Reuters received an emailed bomb warning about an hour before the explosions, signed by Jomo Gbomo, principal spokesman for the Movement for the Emancipation of the Niger Delta (MEND).
In a statement on Saturday, MEND said it regretted the deaths, adding that it had given the security forces five days' notice.
The group has been fighting for years for a greater share of oil revenues for the delta, home to Africa's biggest oil and gas industry, but signed an amnesty with the government last year.
Gbomo said in an email to Reuters on Saturday the attack was meant as a one-off rather than the start of a new campaign.
"It was a symbolic and opportunistic attack intended as a one-off high profile reminder that the injustice in the Niger Delta has not been addressed," the email said.
OIL PRODUCTION UP
Previous MEND campaigns, including pipeline bombings and oilfield raids in the Niger Delta, shut down a significant proportion of the OPEC member's oil output, costing an estimated $1 billion a month in lost revenues at the height of the unrest.
Oil production has risen from about 1.6 million barrels per day before the amnesty to about 2 million as oil companies managed to repair sabotaged infrastructure.
President Goodluck Jonathan, who faces an election next year and who is from the poor delta region, has condemned the attacks and vowed to bring those responsible to justice.
"We know the persons behind this. We know the persons who sponsored this. We are on their trail. They will have a bad date with history," Jonathan said at a meeting of officials from West African regional bloc ECOWAS on Saturday.
Ogar said Henry Okah, a senior member of MEND, had been arrested in South Africa. Police there declined to comment.
Security experts believe Okah, who accepted the amnesty last year after gun-running and treason charges against him were dropped, was at one time the brains behind MEND, although he has denied ever being its leader.
In his email, Gbomo said: "We believe this is a routine questioning and expect him to be released soon."
Although most of MEND's activities have been focused on the creeks of the Niger Delta, it has struck oil facilities offshore and once in the heart of Nigeria's commercial capital, Lagos.
Its attacks have tended to avoid civilian casualties, leading some to question whether the Abuja bombs were the work of a splinter group or might relate to the power struggle brewing ahead of next year's elections.
Jonathan is facing several challengers, including former military ruler Ibrahim Babangida, for nomination as the ruling People's Democratic Party's presidential candidate. (Additional reporting by Felix Onuah, Tiisetso Motsoeneng, Kylie MacLellan, Austin Ekeinde and Nick Tattersall; writing by Ed Cropley; editing by Andrew Dobbie)
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