The Movement for the Emancipation of the Niger Delta (MEND) halted its attacks in Nigeria's oil producing southern region in July to allow for possible peace talks following President Umaru Yar'Adua's amnesty offer to all gunmen. But the two sides have not yet held any formal discussions.
"The Movement for the Emancipation of the Niger Delta resumes its hostilities against the Nigerian oil industry, the Nigerian armed forces and its collaborators with effect from 00:00 hours Friday, October 16," the group said in an e-mailed statement.
MEND, responsible for attacks that have crippled Nigeria's oil industry for the last three years, warned last week that it would "burn down" all previously attacked oil installations.
But the rebel group has been severely weakened after its most prominent commanders and thousands of others accepted clemency and disarmed.
Unrest in the Niger Delta has prevented Nigeria, which vies with Angola as Africa's biggest oil producer, from pumping much above two-thirds of its production capacity.
It costs the country $1 billion a month in lost revenues, according to the central bank, and has helped to push up global energy prices.
But the decline in violence in the creeks of the Niger Delta has already helped bring back some oil production, the oil minister said last week.
Skeptics say that there is little to stop fighters from finding new leaders and resuming attacks. Some residents fear they will return to the creeks unless those who hand over their weapons can quickly find work.
(Reporting by Randy Fabi; Editing by Charles Dick)