A Nigerian militant group based in the oil-producing Niger Delta said on Sunday it had attacked an oil pipeline owned by Italian firm Eni where witnesses said there was a fire late on Saturday.

The 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.

Eni was not immediately available for comment but witnesses said there was a fire on the company's Nembe-Brass pipeline.

The amnesty led thousands of militants to drop arms, join training programmes and collect stipends. Security sources say the remaining gangs in the Niger Delta do not have the capacity to do the damage seen in the past, which at its height cut out 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 of the recent damage caused to Nigeria's oil infrastructure has been from gangs stealing oil, rather than 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 email 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.

The joint military task force (JTF) operating in the Niger Delta said recent unrest stemmed from criminal gangs who wanted expired amnesty benefits.

It should be noted that it is not possible to run an inelastic amnesty programme, Timothy Antigha, spokesman for the JTF in Bayelsa state, said in reaction to the MEND statement.

Unfortunately, people who were never part of the agitation have emerged and want to claim amnesty and its benefits by force ... 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.

Bayelsa, the home state of President Goodluck Jonathan, is due to hold a governorship election next week.

Governors are some of the most powerful politicians in Africa's most populous nation, in some cases controlling budgets bigger than other African nations. The military presence in the state has been beefed up ahead of the February 11 vote.

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.

(Reporting by Tife Owolabi; writing by Joe Brock)