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.