ONITSHA, Nigeria (Reuters) - A Nigerian militant group attacked a pipeline operated by Italy's ENI in the Niger Delta region early on Friday, the militants and a security official said.

"There was an attack on the Obi Obi Brass Pipeline between 1 and 2 am today Friday," said Desmond Agu, commander of the Nigeria Security and Civil Defence Corps in Bayelsa state.

"There is an oil spill at the scene...but the place is not on fire."

The Niger Delta Avengers militant group earlier claimed responsibility for the attack on the pipeline via its Twitter feed. The pipeline is related to the Brass River crude oil stream in Nigeria's Bayelsa state, the site of many attacks over the past month.

The Avengers said the attack hit Agip's major crude oil line but oil traders said there was no immediate indication that flows from Brass River had completely stopped.

ENI did not immediately comment on the attack or its impact on oil production and exports.

ENI's oil infrastructure has been hit previously by militants, and its Brass River oil stream is already under force majeure, though some cargoes had continued to load. One suezmax, the Hrvatska, was expected to load Brass River crude this week, while a second was scheduled to arrive on June 17.

(Reporting by Anamesere Igboeroteonwu in Onitsha and Libby George in London, writing by Ulf Laessing, editing by Angus MacSwan)