LAGOS, Nigeria (CNN) -- Nigerian militants said Monday they had blown up an oil pipeline and captured six crew members of a chemical tanker.
In a statement, the Movement for the Emancipation of the Niger Delta said the Okan manifold was blown up at 8:45 p.m. (3:45 p.m. ET) Sunday. The militants said the manifold carried some 80 percent of Chevron Nigeria Limited's off-shore crude oil to a loading platform.
In a separate action, the group said that three Russians, two Filipinos and an Indian were seized Sunday from the Siehem Peace about 20 miles from the southern port city of Escravos "for disregarding our warning to oil, gas and chemical workers to keep away from the Niger Delta waters."
The group added the action was taken "to serve as a warning to others that there are root issues that have to be resolved with the Nigerian government before normalcy can resume," such as the return of displaced civilians to their ancestral homes and compensation for damages.
The Movement for the Emancipation of the Niger Delta has declared an "all-out war" on the Nigerian government. The militant group demands that more of Nigeria's oil wealth be reinvested in the region instead of enriching those whom the militants consider corrupt politicians.
Col. Rabe Abubakar, spokesman for the Nigerian military's Joint Task Force, said he had no details about the pipeline attack or the seized ship, but described such attacks as "purely economic sabotage," requiring no great skill to carry out.
"They are attacked when no one's guarding the place, so even a small child can blow up a pipeline and run away -- no one is there to guard them," Abubakar said.
In a statement, Chevron confirmed the breach and said no one was hurt.
Sunday's pipeline attack came hours after the militant group said it had attacked another oil facility, "leaving total destruction in its wake."
In a statement, it said it had "lashed out at the Shell Well Head 20, located at Cawthorn Channel 1" at 3 a.m.
Royal Dutch Shell did not respond to calls for comment.
Repeated attacks on oil platforms have disrupted oil operations in Nigeria in recent years.
Shell said last week that there had been eight attacks at Shell Petroleum Development Co.'s facilities in the last four weeks, dropping SPDC's production to 140,000 barrels a day. In 2008, it was at 850,000 barrels a day. That represents a drop of 84 percent.
SPDC is a joint venture with the Nigerian government.
Last month, Amnesty International said that pollution and other environmental effects 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."
But the state oil company said it was local communities that cause much of the environmental damage by vandalizing pipelines for monetary gain.
"We take environmental damage very seriously," said Levi Ajuonoma, a spokesman for Nigerian National Petroleum Corp.
"Pipeline damage is a major cause of pollution," Ajuonoma said, blaming "communities who... vandalize pipelines and make claims on the oil company operating in the area."
The Niger Delta is a region in Nigeria consisting of nine oil-producing states. Covering 46,500 square miles (75,000 square kilometers), it is about the same size as the Czech Republic or Pennsylvania, according to the U.N. Development Program.
CNN's Christian Purefoy contributed to this report from Lagos.