Ethnic fighting has resurfaced in Nigeria's oil-rich Niger Delta. Tribal clashes last March forced the withdrawal of major oil companies from the area.

Fighting erupted Friday night and continued into the early hours of Saturday between two ethnic groups, Itsekiris and Ijaw residents of the delta.

According to on the ground reports, this is the most serious fighting in the area since March. Then, ethnic clashes in the region led to dozens of deaths, and forced multinational oil giants to curtail operations in the area.

Tensions between the Itsekiris and the Ijaw communities have remained high in recent months, with intermittent reports of violence.

The Niger Delta is an unstable area of Nigeria, and inter-ethnic clashes are common - often access to oil revenue is the trigger for the violence.

Pipelines are regularly vandalized by impoverished residents, who risk their lives to siphon off fuel. Vandalism is estimated to result in thousands of barrels of crude oil wastage every day - a loss to the Nigerian economy of millions of dollars each year. Nigeria is the world's sixth largest oil-producing nation. However, mismanagement and successive military governments have left the country poverty-stricken.