Nigeria's most prominent militant group, the Movement for the Emancipation of the Niger Delta, or 'MEND', has claimed responsibility for a third day of violence in the southern oil producing region.   Sarah Simpson reports from Lagos the militants say their attacks are part of an "oil war" and have told all oil workers to vacate the region for their own safety.

MEND militants brandish weapons (file photo

The Niger Delta entered a third day of violence, as MEND militants claimed responsibility for an attack on an oil-pumping station operated by Royal Dutch Shell.

Nigerian military spokesman, Lieutenant Colonel Sagir Musa told reporters that militants in speed boats - armed with rocket launchers and dynamite - attacked the oil facility in a pre-dawn assault.

Musa says no soldiers were injured in the hour-long gun fight that followed.  Independent verification of casualty figures is not available.

Military and militant sources say the Shell oil-pumping facility was seriously damaged in the attack.  Shell has yet to confirm any impact on their operations.

This latest MEND attack follows a Sunday statement declaring an "oil war" and demanding all oil workers to leave the Niger Delta for their own safety.

Since MEND emerged almost three years ago, it has carried numerous attacks on oil infrastructure and foreign oil workers in the Niger Delta.  Most non-essential oil personnel have been evacuated or relocated out of the region.

MEND says it is fighting for a greater share of Nigeria's vast oil revenues to go to the region the produces the oil - the Niger Delta.

Observers say MEND's declaration of war could mark a new level of instability in the delta.  Local newspapers are reporting that the Nigerian military has resolved to take a tougher line with the delta militants.

MEND say it has launched its war in response to a weekend raid by the Nigerian military on militant fighter camps.  Militants say the military launched a marine and air offensive on one of their positions on Saturday.

MEND is an umbrella for a host of disparate armed gangs that operate out of the delta.  Despite hard-hitting rhetoric from the militants, it is not clear to what extent, if any, some of these gangs share MEND's stated aims.

Some observers in Nigeria say the militants are more interested in enriching themselves through crime than fighting a politicized anti-government campaign.

The Nigerian government has repeatedly described the militants as criminals.

Nigeria is the eighth-largest oil exporting nation in the world, and a member of OPEC.   Militant activity in the Niger Delta has cut oil output by as much as 25 percent and helped force up oil prices worldwide.