YENAGOA, Nigeria (Reuters) - A militant group said on Tuesday it attacked a pipeline operated by a subsidiary of Nigeria's state oil company in the country's southern Delta region, just a day after the most prolific rebel group in the restive energy hub said it had halted hostilities.

OPEC member Nigeria has seen its oil output fall by around 700,000 barrels a day to 1.56 million bpd due to attacks on oil pipelines in the southern energy hub, home to much of the country's oil and gas wealth, since the start of the year.

The Niger Delta Greenland Justice Mandate said it attacked the Ogor-Oteri pipeline in Delta state, operated by Nigerian Petroleum Development Company (NPDC) and Nigerian energy company Shoreline, at around 03:00 a.m. (0200 GMT) on Tuesday.

Niger Delta Avengers, the group that claimed responsibility for most attacks in the impoverished region where militants want a greater share of the country's oil wealth, said on Monday it had halted hostilities.

"The Niger Delta Greenland Justice Mandate remains underailed on its mission to getting justice for the people," said the group, previously unknown before an attack on Aug. 11.

The group also criticized other militants for participating in talks with the government. It said others had merely sought to "harass the Nigerian state and the oil multinationals into parting with money".

Community leader Lucky Sorue, chairman of the Urhobo committee on oil and gas, said locals heard an explosion and he visited the blast site early on Tuesday.

"When we visited the scene we saw that the pipeline was badly damaged and blown open with explosives," he said.

Garba Deen Muhammad, a spokesman for the state oil company NNPC, said the attack was being investigated.

(Reporting by Tife Owolabi and Anamesere Igboeroteonwu; Writing by Alexis Akwagyiram; Editing by Louise Heavens and Susan Thomas)