Nigeria's main militant group said it had blown up a well-head in a Royal Dutch Shell
The Movement for the Emancipation of the Niger Delta (MEND) accused the military of going on a punitive expedition to hunt down suspected militants in the Agbeti community of Delta state after Yar'Adua's amnesty proclamation.
In response ... (operation) Piper Alpha continued its rampage on the Nigerian oil industry by blowing up the second remaining well-head of the Shell Afremo offshore oil fields in Delta state, MEND said in a statement e-mailed to media.
The military denied carrying out any such campaign.
Our troops did not carry out any operation in Agbeti. This is a lie, propaganda by these miscreants to justify their attacks on isolated oil facilities, said Colonel Rabe Abubakar, spokesman for the joint military taskforce in the Niger Delta.
A Shell spokeswoman said it was investigating reports of an attack on its Afremo platform B facility, which had already been shut down following an attack on the Trans Escravos pipeline in February.
Afremo was one of the sites MEND also said it had attacked in a triple raid on Sunday. It described the field as being 14 miles from an export terminal through which crude oil from Shell's Forcados fields is pumped.
A senior industry source said at the time the location was not a deepwater installation, but a facility located in or close to the mangrove creeks, where pipelines and equipment run across broad stretches of water.
BILLIONS IN LOST REVENUE
Yar'Adua on Thursday offered the amnesty to gunmen who laid down their weapons during a 60-day period ending on October 4, in a bid to end years of unrest which have cost Africa's top oil exporter billions of dollars in lost revenue.
Pipeline bombings, attacks on oil and gas installations and the kidnapping of industry workers over the past three years have prevented Nigeria from pumping much above two thirds of its installed capacity of 3 million barrels per day of oil.
The supply disruption has at times helped push world energy prices higher and cost Africa's most populous nation, which relies on crude oil for 90 percent of its foreign earnings, tens of millions of dollars a day.
MEND's latest campaign of sabotage, which began just over a month ago and which it has dubbed Hurricane Piper Alpha, has already forced at least 133,000 barrels per day (bpd) of production to be shut down.
It has again had an impact on global energy prices, helping push oil over $71 a barrel on Friday.
One faction leader, Ateke Tom, has indicated he would consider taking part in an amnesty while a lawyer for Henry Okah, the suspected leader of MEND who is on trial for treason, has said he hoped his client would be covered by the proposal.
But the unrest in the delta is not a straightforward political struggle. Skeptics question whether an amnesty alone will be enough to halt opportunistic attacks, crude oil theft and kidnapping, much of which generates large amounts of money for armed gangs and the disenfranchised youths they recruit.
(Additional reporting by Randy Fabi in Abuja and Austin Ekeinde in Port Harcourt; Editing by Alison Williams)