LAGOS, Nigeria (CNN) -- Militants in Nigeria's oil-rich southern delta region said they killed six government soldiers after the military attacked one of its camps on Thursday.
The Movement for the Emancipation of the Niger Delta, in an e-mail, said three military gunboats attacked one of its camps around the Ke River in the country's Rivers state.
The group said the gunboats were repelled, with six soldiers dying and three militant fighters wounded in the skirmish.
There was no immediate reaction from the government.
Nigeria is Africa's largest crude oil producer and the fourth-largest supplier of oil to the United States. MEND has demanded that more of the country's oil wealth be pumped into the region instead of enriching foreign investors, and the militants have been attacking oil pipelines in retaliation against government forces, limiting the amount of crude oil that can leave the country.
MEND -- the largest rebel group -- has targeted foreign oil companies since 2006. It has bombed pipelines and kidnapped hundreds of foreign oil workers, typically releasing them unharmed, sometimes after receiving a ransom payment.
MEND hopes to secure a greater share of oil wealth for people in the delta, where more than 70 percent of the population lives on less than a dollar a day.
Its attacks on oil facilities have taken a toll.
"Anytime a pipeline is affected, anytime any production gets shut down, you see oil prices jump up one or two dollars a barrel just because there is no slack in the system," said Jim LeCamp, a senior vice president with RBC Wealth Management, which manages assets for wealthy clients worldwide.
Exxon and Shell are two of several companies that have been extracting 2 million barrels of oil a day in Nigeria. Recent rebel attacks on oil pipelines in the Niger Delta have cut overall production by roughly 10 percent -- meaning 200,000 fewer barrels of oil on some days.
That decrease in production comes at a time of increased demand from oil-hungry regions such as China, Russia and Latin America.
"Anytime there's a disruption there, it really affects the system," LeCamp said in a recent interview with CNN.