Mujahid Dokubo-Asari told journalists on Sunday his group had also decided to attack oil installations and personnel of the Italian oil company Agip, accusing the company of lending its helicopters to the military to spy on rebel positions.
Oil production has not yet been affected by the intensifying conflict in Africa's top oil producer, but companies fear a repeat of last year's uprising by members of the Ijaw tribe, which forced them to shut temporarily 40% of the country's 2.5 million barrel per day output.
"We have decided to declare Operation Locust Feast which will cover the whole Niger delta. It is going to be an all-out war against the Nigerian state. Now the whole Ijaw nation will be fighting against the Nigerian state," Asari told Reuters by satellite phone.
The conflict has until now been focused around the eastern delta near Port Harcourt, which pumps about half of Nigeria's oil. The other half comes from the western delta, also inhabited predominantly by Ijaws and scene of last year's rebellion.
The government has launched a major military offensive against Asari, using fighter jets and helicopter gunships to bomb his camps last week.
Asari says his Niger Delta People's Volunteer Force, which he said had 168,000 members, will fight until the government agrees to call a Sovereign National Conference, where the country's ethnic groups can renegotiate the terms of the Nigerian federation.
The fighters are demanding
independence from Nigeria
He says he is fighting for the inhabitants of the Niger delta, most of whom live in abject poverty despite having all the nation's oil reserves. The state government has called him a gangster fighting for control of smuggling routes used by oil thieves.
"We were forced into Nigeria by the British colonialists. We are not Nigerians - there is no such nation as Nigeria," Asari said. "Until there is a Sovereign National Conference to decide these issues, we have no choice but to fight until sovereignty is in our hands."
Asari said his forces would target Italian oil company Agip, a unit of ENI, accusing it of lending the military its helicopters to spy on his camps.
"Agip loaned the Nigerian state a helicopter to spy on our positions. After that they came with fighter jets and helicopters to bomb us."
"Since Agip has joined the Nigerian state, we will attack them if we see them. We will attack their installations and personnel because they have joined the war on the side of the
Nigerian state," Asari said.
Agip spokesmen in Nigeria and Italy were unavailable for comment.
The Nigerian Agip Oil Company, a joint venture in which ENI has 60% equity, operates four main onshore blocks in the Niger Delta region where ENI's production is currently concentrated.
ENI has been operating in Nigeria since 1962. In 2002, the fields where ENI is operating generated about 10% of Nigeria's total annual oil production.
Amid brewing tensions in Nigeria's delta, Shell last week evacuated 235 non-essential staff from the conflict zone.