Nigerian militants clashed with soldiers in the oil-rich Niger Delta before warning firms to evacuate staff by the weekend or face the "arrival of an imminent hurricane."
The Movement for the Emancipation of the Niger Delta (MEND), Nigeria's main militant group, said it had raided two military bases overnight in the oil-rich southern region.
MEND said the raids followed military attacks on two of its own camps in Delta state on Wednesday morning. It claimed to have sunk two army gunboats "with several casualties on the side of the army" in the ensuing battle.
A spokesman for the special military body in the volatile Niger Delta region, the Joint Task Force, confirmed Wednesday's clash but denied the army lost any men.
"They ambushed our people. We had to defend ourselves. Only two of our soldiers were wounded in the attack. We did not record any casualty at all. It is sheer propaganda on their part," Colonel Rabe Abubakar told AFP.
MEND said it had launched "pre-emptive simultaneous attacks on two military Joint Task Force marine bases in Delta state in response to a planned punitive invasion on some protesting oil communities.
"Oil workers are advised to don the cloak of common sense and evacuate all oil facilities in the Niger Delta before the arrival of an imminent hurricane," the MEND statement warned.
|A Nigerian separatist militant in southern Nigeria|
The group extended an earlier ultimatum for staff to leave by 48 hours until Saturday.
"Effective 0000 Hrs on Saturday, May 16, 2009, the entire Niger Delta region will be declared a no-fly zone to helicopters and float planes operating on behalf of oil companies.
"All freedom fighters in the Niger Delta have been placed on alert to defend their positions and unleash a horrible toll on the oil industry and the Nigerian economy."
MEND, which has been blamed for scores of attacks on oil installations and kidnappings of foreign oil workers, ended its unilateral ceasefire in January.
They say they are fighting for a fair distribution of oil wealth to local communities in the impoverished Niger Delta region.
The unrest has helped Nigeria lose its position as Africa's leading crude exporter to Angola. Nigerian oil output has fallen by about a quarter since 2006, largely as a result of militant activities in the Delta region.
A member of the Organisation of Petroleum Exporting Countries (OPEC), Nigeria relies on oil for about 99 percent of its export earnings and about 85 percent of government revenues, according to the World Bank.