Three people have been shot dead in the Nigerian state of Bayelsa amid growing tension over how the region's oil wealth is shared out.

On Wednesday the authorities in the oil-producing Delta region, imposed a dusk-to-dawn curfew to prevent violence after militants from the local Ijaw community gave oil companies an ultimatum to pull out.

The ultimatum, delivered two weeks ago, expired on Wednesday.

Over the past few months, the activities of oil companies in the Delta region have frequently been disrupted by local activists.

Shell, which is the largest oil company operating in Nigeria was forced to suspend operations in Ogoniland in 1993, following repeated sabotage.

Any disruption to supplies from lands of the four million Ijaws, could cripple both Shell's operations in Nigeria and the country's economy, which remains dependent on income from oil