Nigerian militants have attacked an oil pipeline, breaking a tenuous ceasefire with the government over the long absence of its ill president.
Militants armed with assault rifles, machine guns and rocket launchers attacked a major crude oil pipeline operated by Shell and Chevron in Nigeria's Rivers State, the Movement for the Emancipation of the Niger Delta said in a statement.
Group spokesman Jomo Gbomo said the group would consider the unconditional cease-fire agreement it made with the government on October 25 void for the next 30 days.
The attack comes after President Umaru Yar'Adua held formal peace talks with the group and many militants put down their arms as part of a government amnesty.
While the militants have broken cease-fires in the past, the attack highlights the Nigerian government's struggles with Yar'Adua's weeks-long absence as he tries to overcome a reportedly serious heart condition.
Mr Gbomo said the attack occurred in part because of government officials slowing peace talks because of Yar'Adua's absence.
"A situation where the future of the Niger Delta is tied to the health and well-being of one man is unacceptable," the statement read.
Spokesmen for Chevron and Shell did not immediately respond to calls for comment.
The militants have attacked oil installations, kidnapping petroleum company employees and fighting government troops since January 2006.
They demand that the federal government send more oil-industry funds to Nigeria's southern region, which remains poor despite five decades of oil production.
The attacks have cut Nigeria's oil production by about a million barrels a day, allowing Angola to surge ahead as Africa's top oil producer.
Yar'Adua, long troubled by a kidney ailment and poor health, traveled out of the country several times for what his advisers said were medical checkups before he left Nigeria for Saudi Arabia on November 23.
He was admitted into the hospital the next day. As questions mounted, his physician released a statement saying Yar'Adua suffered from acute pericarditis, an inflammation of the sac surrounding the heart that can cause a fatal complication.
Yar'Adua did not formally appoint a leader in the West African nation in his absence, sparking constitutional confusion and calls for him to resign if he's too sick to hold the office.
