LAGOS (AFP) -- The most prominent militant group in oil-rich southern Nigeria on Sunday said it had declared an ""oil war"" and threatened all international industry vessels that approach the region.

The Movement for the Emancipation of the Niger Delta ( MEND ) said in an email to the media it has code-named its operation Hurricane Barbarossa.
""About 0100 Hrs, today ... Hurricane Barbarossa commenced with heavily armed fighters in hundreds of war boats filing out from different MEND bases across the Niger Delta in solidarity to carry out destructive and deadly attacks on the oil industry in Rivers state,"" the group said.
The ""war"" was in response to what it says were unprovoked aerial and marine attacks by the army Saturday on one of its positions.
A Nigerian army officer, Lieutenant-Colonel Musa Sagir, earlier Sunday confirmed what he said was an aborted attack on the Robertkiri facility operated in Rivers state by U.S. oil giant Chevron.
Chevron confirmed a shooting incident at the Robertkiri facility but said it did not have information to suggest the attack was directed specifically at the company. It said no expatriate workers were involved in the incident and production was not impacted.
""As a result of ongoing pipeline repair work the Robertkiri facility ... had been shut-in prior to the incident. The shooting incident has not had any additional impact on current levels of ... production,"" company spokesman Scott Walker said in an email.
MEND however said that during the Chevron attack it ""intercepted, killed and dispossessed of their weapons 22 well armed soldiers"" who were sent in as reinforcements.
Chevron said that while none of its employees was hurt as a result of the shooting, initial reports suggest that two employees of a local marine vessel supply company, Dahnariq Nigeria Ltd -- which supplies small vessels to Chevron -- might have died.
So far there has been no independent confirmation of other attacks.
Royal Dutch Shell said it was still investigating reports of attacks on its facilities.
""The operation will continue until the government of Nigeria appreciates that the solution to peace in the Niger Delta is justice, respect and dialogue,"" MEND said.
The group warned all vessels to stay on the high seas and not to come into port. The Niger Delta is an area of creeks and swamps the size of Scotland located on the Gulf of Guinea.
""All international oil and gas loading vessels entering the region are warned to drop anchor in the high sea or divert elsewhere until further notice. Failure to comply is taking a foolhardy risk of attack and destruction of the vessel.""
It also reiterated the warning it issued Saturday to oil companies telling them to evacuate their staff from field facilities.
""Again, we are asking that oil companies evacuate their staff from their field facilities because the brief is not to capture hostages but to bring these structures to the ground,"" MEND said.
MEND has made similar dramatic threats in the past about destroying oil facilities and halting oil exports from the region totally but has not so far made good on them, although it has kept up its campaign of kidnappings and sabotage.
Technically however the group is capable of very ambitious attacks. In June its fighters attacked Bonga, Shell's flagship field, 120 kilometers (74 miles) off the coast of Nigeria. Until that attack deep offshore facilities had been thought to be out of reach of militant groups.
Earlier this week Nigerian President Umaru Musa Yar'Adua announced he was creating a ministry for the Niger Delta in an attempt to bring peace to the region.
Militants dismissed the plan, saying other ministries already in existence had done little to improve life for Nigerians.
The kidnapping of oil workers and sabotage of oil facilities have reduced Nigerian crude production by about a quarter over the past two years. The west African producer currently exports around two million barrels of oil daily.
Unrest in the Niger Delta has also cost Nigeria its position as Africa's biggest oil producer. In April it was overtaken by Angola, according to the Organization of Petroleum Exporting Countries (OPEC).