Advising all oil companies to shut production by 1 October, the Niger Delta People's Volunteer Force also advised foreigners to leave the delta in a communique issued after a meeting of its central command on Monday.
The rebel group's leader, Mujahid Dokubo-Asari, accused Royal Dutch/Shell, Nigeria's largest oil producer, and Italy's Agip, a unit of ENI, of "collaboration with the Nigerian state in acts of genocide against our people".
Asari said his group would not attack oil installations because it did not want to pollute the delta environment, but foreign oil workers would be targeted.
Nigeria currently produces 2.3 million barrels per day. The warning had an immediate effect on oil prices.
In New York, crude oil futures jumped 36% in electronic trading to $50 a barrel, the highest in the 21 years oil futures have traded on the exchange after the announcement from the group.
"Anyone who assists the Nigerian state make money in Ijawland (the delta) will be seen as a collaborator and an enemy and will be targeted"
Rebel group leader, Mujahid Dokubo-Asari
Asari said the group's offensive would continue until the government agreed to negotiate self-determination for the Ijaw people, who form a majority in the delta.
The delta violence has so far had a minimal effect on oil production in the world's seventh largest exporter, but companies fear a repeat of last year's Ijaw rebellion which forced them briefly to shut 40% of production.
"All foreign embassies should withdraw their citizens from the Niger delta until the resolution of the fundamental issues," he added.
He said the Niger Delta People's Volunteer Force would not take responsibility for any harm to foreign nationals and advised the government and embassies to withdraw their citizens.
"That means they have to close their facilities," he said. "Anyone who assists the Nigerian state make money in Ijawland (the delta) will be seen as a collaborator and an enemy and will be targeted," Asari added.
Operations to continue
Royal Dutch/Shell group said it saw no reason to discontinue oil operations in Nigeria's delta.
Shell has received similar rebel
threats in the past
A spokesman said the company had received similar threats in the past and had already taken some precautionary measures, including evacuating 235 non-essential staff from two oilfields, to address specific threats to its personnel.
"We have received threats like this in the past. We have made a precautionary withdrawal from areas where we see a security risk and we are minimising boat movements," the spokesman said.
"We are watching developments, but for now we see no reason not to continue our operations."