UPDATE: 2:15 p.m. EDT -- The aftermath of a late night attack at a major Chevron-operated offshore platform in oil-rich Nigeria is cutting into the country's crude production, the U.S.-based energy company told International Business Times. Although no employees were injured in the attack, Chevron Nigeria Limited has been forced to shut-in the affected Okan facility in the Niger Delta region, which churns out tens of thousands of barrels a day.

"Approximately 35,000 barrels per day of Chevron’s net crude oil production in Nigeria are impacted," a Chevron Nigeria Limited spokesperson said in a statement.

Original story:

Suspected militants attacked a Chevron-operated offshore oil facility in southern Nigeria late Wednesday, resulting in an oil spill. There were no injuries and all employees have been accounted for, the U.S.-based energy company told International Business Times.

“Its Okan offshore facility in the Western Niger Delta region was breached by unknown persons,” a Chevron Nigeria Limited spokesperson said in a statement. “The facility is currently shut-in and we are assessing the situation, and have deployed resources to respond to a resulting spill.”

Chevron produces some 240,000 barrels of crude oil per day in the West African nation. Its Okan platform is a joint venture with the state-run Nigerian National Petroleum Corp., according to the company’s website.

The incident marked the latest in a string of attacks on oil facilities in Africa’s top oil producer. A rebel group called the Niger Delta Avengers claimed responsibility for the late night raid, saying it blew up the major platform.

“This is what we promised the Nigeria government since they refuse to listen to us,” the group said in an online statement obtained by IBT. “Now we are taking the fight out of the creeks of the Niger Delta. We are taking it to Abuja and Lagos now.”

The group threatened anyone who tries to repair the blast site, saying no work shall be done until their demands are met. The Niger Delta Avengers previously claimed responsibility for an attack on a Shell-operated oil pipeline in February which shut down the 250,000 barrel-per-day Forcados export terminal. The rebels say they want a greater share of lucrative oil revenues, which account for some 70 percent of national income.

“We want to pass this message to the all international oil companies operating in the Niger Delta that the Nigeria military can’t protect you[r] facilities. They should talk to the federal government to meet our demands else more mishaps will befall their installations,” the group said in the statement Wednesday.

Rebels largely belonging to a group called the Movement for the Emancipation of the Niger Delta wreaked havoc on pipelines and facilities in Nigeria’s oil-rich southern swampland until 2009 when then-President Umaru Musa Yar’Adua offered an amnesty deal to thousands of militants, whose vandalism, theft and attacks in the six Niger Delta states had cost the country a third of its oil production. The rebels agreed to lay down their arms in return for an unconditional pardon and stipend.

The multimillion-dollar amnesty program continued under President Goodluck Jonathan, and ex-rebels had threatened to renew attacks if he lost re-election in March last year. After defeating Jonathan in the election, Nigerian President Muhammadu Buhari extended the amnesty program but angered the rebels by ending generous pipeline protection contracts.

The Niger Delta Avengers is thought to involve supporters and former rebels of the Movement for the Emancipation of the Niger Delta group who are upset by the changes, Agence France-Presse reported. Wednesday night’s attack on the Chevron-operated facility stirred growing fears of a revived militant campaign in the southern oil-producing region during a time the Nigerian government is also faced with an Islamic insurgency by Boko Haram in the northeast.