LAGOS , Nigeria ( CNN ) -- A Nigerian militant group claimed Wednesday it sabotaged oil pipelines in the country 's oil-rich southern Niger Delta , but the country 's military denies the assertion . File image of armed MEND militants in Niger Delta region of Nigeria . The Movement for the Emancipation of the Niger Delta ( MEND ) said in an e-mail message to reporters that the `` major Shell and Agip crude trunk lines in Bayelsa state '' were struck . `` The Agip pipeline which connects the Agip Brass terminal was sabotaged at Nembe creek while the Shell Nembe creek line was done at Asawo village , '' MEND said . Shell said it is investigating reports of an attack on the Nembe creek pipeline and Agip could not be reached for comment . Rabe Abubakar , spokesman for the Nigerian military 's Joint Task Force , said `` the militants are telling lies '' and `` there is no iota of truth in what they are saying . '' Their claims against the Shell pipeline `` are not true , '' Abubakar said , explaining that explosives were hurled at the pipeline but the explosion was limited and it did not destroy the line . `` There was an attempt by them to blow up an Agip pipeline around 3 a.m. , but the soldiers protected the place and the militants fled , '' Abubakar said . Explosives were found on a well and an explosives expert was brought in to remove them , he added . MEND -- which has declared an `` all-out war '' on the government -- demands that more of Nigeria 's oil wealth be reinvested in the region , instead of enriching those whom the militants consider corrupt politicians . But fighting has continued despite Nigerian President Umaru Yar'Adua 's recent call for an amnesty for the militant groups , an offer that stays open until October 4 . Under the amnesty proposal , militants must hand in their weapons and take part in government rehabilitation programs . Also on Wednesday , the military said three people were seized for trying to blow up a pipeline at the Forcados River . But MEND said the military `` arrested two repentant armed youths who approached them to take advantage of the government 's amnesty offer . '' `` We are learning that there are about 11 of such cases currently languishing in detention inside the JTF headquarters in Warri , '' MEND said . Last month , Amnesty International said that pollution and other environmental impacts from the oil industry in the Niger Delta are creating a `` human rights tragedy '' in which local people suffer poor health and loss of livelihood . Governments and oil companies are failing to be accountable for the problems , Amnesty said in its report , called `` Petroleum , Pollution and Poverty in the Niger Delta . '' Covering 46,500 square miles ( 75,000 square km ) , the Niger Delta is about the same size as the Czech Republic , according to the United Nations Development Programme . An area of rich biological diversity , the region contains the world 's third-largest wetland with the most extensive freshwater swamp forest , according to the UNDP . More than half the area contains creeks and small islands , while the rest is rain forest , the UNDP says . At the same time , the Niger Delta produces the oil wealth that accounts for the bulk of Nigeria 's foreign earnings , the UNDP says . Earlier this week , MEND said its fighters had blown up an oil pipeline and captured six crew members of a chemical tanker . MEND is now saying it has released the ship and the military says it secured the vessel . It is not clear whether the three Russians , two Filipinos and the Indian seized remain in custody . MEND told CNN that `` to their knowledge , '' the crew is no longer being held hostage . CNN 's Christian Purefoy contributed to this report .
Nigerian militant group says it struck Shell and Agip crude trunk lines . Shell said it is investigating reports of an attack on the Nembe creek pipeline . The U.S. State Department has warned Americans to avoid travel in Nigeria because of a recent spate of kidnappings by suspected Boko Haram militants.