Members of Movement for the Emancipation for the Niger Delta in Nigeria's Niger Delta area (file photo)

Nigeria's most prominent militant group said on Wednesday it had attacked an oil-pumping station owned by Chevron in the conflict-prone delta region.

The Movement for the Emancipation of the Niger Delta, MEND, said in an e-mail statement that the overnight strike was a direct response to the military offensive currently under way in the region. Chevron has confirmed the raid.

It was the second retaliatory attack since last month when Nigerian security forces began one of the biggest operations in years, bombarding militant camps from the air and sea before sending troops to hunt down rebels.

MEND had claimed responsibility for a May 25 pipeline attack that interrupted delivery of 100,000 barrels of oil a day.

Nigeria, which depends heavily on oil sales, says government revenue has fallen by at least 30 percent in the first three months of this year. Odein Ajumogobia is the deputy oil minister.

"Nigeria has a production capacity of 3.2 million barrels a day. Today, we are down to about less than half of that in terms of production. Over one million barrels are shut in as a direct result of security issues in the Niger Delta. That is something that should concern all of us."

Nigeria has struggled to contain the Movement for the Emancipation of the Niger Delta, which started attacking the country's oil industry and kidnapping oil workers just over three years ago.

The group says it is fighting for greater development and better living environment after decades of neglect.

The military has bombed militant strongholds in the creeks surrounding Warri in recent weeks in a campaign to wipe out militancy.

MEND has rejected an amnesty offer issued by President Umaru Yar'Adua last week.