(CNN) -- Three attacks were made on Royal Dutch Shell oil facilities in Nigeria on Sunday, according to a company spokesman who said details were not immediately available.



Investigating the attacks will be difficult because they happened in remote areas, Royal Dutch Shell says.



The attacks were against pipelines in the eastern part of the Niger Delta in Nigeria, said the spokesman, Rainer Winzenried.



"Shell is investigating the impact on facilities, the environment and the production capabilities," he said.



The attacks happened in remote areas, making investigations difficult, he said, adding that the company would not send in investigators until it was certain the area was secure. It was not known whether there were any casualties, he said.



The pipelines are part of a Shell joint venture that provides oil to several companies, Winzenried said. Shell runs the venture, and Nigeria is the operator.



Winzenried refused to speculate on who was behind the attacks, but Nigeria's main militant group -- the Movement for the Emancipation of the Niger Delta, or MEND -- said it had attacked an offshore facility earlier Sunday and that "the structure is ... engulfed in fire."



Winzenried had no information about that claim.



MEND, which demands a fairer distribution of Nigeria's oil wealth, claimed Friday that it destroyed a pipeline owned and operated by the Italian gas company Agip, but Agip has not confirmed that report.



Earlier in the week, MEND claimed to have destroyed Royal Dutch Shell's main trunk line in Bayelsa state and a Chevron oil station in the delta region. Shell confirmed an attack on that pipeline and said it had shut it down to avoid an environmental impact. Chevron, which halted its onshore operations in the region last month, said it was investigating.



Last month, the militant group declared an "all-out war" on the government after what it said was a deadly bombing raid on civilians.



It is not the first declaration of war by MEND, which demands that more of Nigeria's oil wealth be invested in the region instead of enriching those whom the militants consider corrupt politicians.



The militant group declared war against the government in September for what it said were unprovoked attacks. At that time, MEND destroyed several oil facilities, forcing Nigeria to cut its oil exports by as many as 1 million barrels of oil per day, or 40 percent.
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