* Niger Delta militants took up amnesty in 2009
* Military blames criminal gangs for attack
* Oil-producing Bayelsa state holds vote next week (Adds ENI confirmation, writes through)
By Tife Owalabi
YENAGOA, Nigeria, Feb 5 (Reuters) - A Nigerian militant group based in the oil-producing Niger Delta said it attacked an oil pipeline owned by Italian firm Eni on Sunday, a strike the military said was the work of criminal gangs.
Witnesses reported a fire on the oil and gas group's Nembe-Brass pipeline late on Saturday, and ENI said the damage would mean the loss of about 4,000 barrels of oil equivalent a day.
A statement sent to media said it was from the Movement for the Emancipation of the Niger Delta (MEND), formerly Nigeria's main militant threat and responsible for years of attacks on the oil industry until a 2009 amnesty.
Under the amnesty thousands of militants gave up their weapons, joined training schemes and drew stipends. Security sources say remaining gangs in the Niger Delta do not have the capacity to do the damage seen in the past, which at its height cut more than a third of the OPEC-member's output.
Several false threats purporting to be from MEND have been sent in the past and most recent damage caused to Nigeria's oil infrastructure has been done by gangs stealing oil for illicit refining and sale, rather than due to militant strikes.
"On Saturday the 4th of February at 1930hrs, fighters of the Movement for the Emancipation of the Niger Delta (M.E.N.D) attacked and destroyed the Agip (ENI) trunk line at Brass in Bayelsa State in the Niger Delta region of Nigeria," the emailed statement said.
"This relatively insignificant attack is a reminder of our presence in the creeks of the Niger Delta and a sign of things to come."
Bayelsa, the home state of President Goodluck Jonathan, is due to hold a governorship election next week.
A falling out between him and former governor Timipre Sylva, who was barred from running again on the ruling party ticket, has degenerated into a slanging match in local media.
Such disputes often trigger a spike in violence in the volatile Delta, although no one suspects this pipeline attack to be directly linked to the row.
The joint military task force (JTF) operating in the Niger Delta said recent unrest stemmed from criminal gangs who wanted expired amnesty benefits.
"Unfortunately, people who were never part of the agitation have emerged and want to claim amnesty and its benefits by force," Timothy Antigha, spokesman for the JTF in Bayelsa state, said in reaction to the MEND statement.
"The JTF advices Niger Deltans to be mindful of people who are out to swindle them by wrongfully appropriating the identity of the erstwhile leadership of MEND to curry sympathy for their selfish and criminal interests."
The military presence in the state has been beefed up ahead of the Feb. 11 governorship vote.
Governors are some of the most powerful politicians in Africa's most populous nation, in some cases controlling budgets bigger than those of entire nations.
Jonathan can ill-afford unrest in his home region as he is already struggling to cope with almost daily violence carried out by radical Islamist sect Boko Haram in northern Nigeria. (Additional reporting by Stephen Jewkes in Milan and Austin Ekeinde in Port Harcourt; Writing by Joe Brock; Editing by Tim Cocks)