In Washington, State Department spokesman Sean McCormack could not confirm Carter's potential mediation role but said there were already "mechanisms" in place to deal with political grievances in the Niger Delta.
"We believe the Nigerian government should also avail itself to those mechanisms," said McCormack who indicated some irritation with Carter's diplomatic role there.
The State Department strongly opposed Carter's recent meetings with the Palestinian militant group Hamas and advised the former president against seeing them.
OIL JITTERS
The bombing of a Royal Dutch Shell flowstation in the southern Nigerian state of Bayelsa on Saturday - which caused little damage to oil infrastructure - marked MEND's fifth strike in just over a month. The attacks are expected to worsen with the trial of militant leader Henry Okah beginning next month, analysts say.
Oil hit a record high of $122 a barrel, lifted by fears of fresh militant strikes in Nigeria, supply concerns in Iran and a forecast from Goldman Sachs that it may hit $200 a barrel due to lagging supply growth.
MEND has accused Nigerian authorities of mistreating Okah, who was deported from Angola in February, and denying him access to his lawyers.
"There is definitely a link to the Henry Okah trial in the resurgent violence," said one security analyst in Nigeria. "How it develops will depend on how they treat Okah and the final decision at the trial."
The militant group, which is split between a number of different factions, dismissed the stalled Niger Delta Summit organized by President Umaru Yar'Adua in an effort to bring peace to the vast, lawless swampland. It said it would not attend a meeting later this year in the capital Abuja.
"The Niger Delta Summit is failing because the government is talking to the wrong people," said Rolake Akinola, senior analyst for West Africa at Control Risks.
"It is a problem of Yar'Adua's leadership style."
