In Nigeria, the army is trying to restore order following ethnic unrest that has disrupted oil production in the Niger River delta.
Nigerian army officials say they have cordoned off much of the area where fighting between ethnic Ijaws and army troops has prompted foreign oil companies to halt operations.
Ijaw militants are threatening to attack oil facilities to press their demand greater political representation.
The fighting erupted earlier this month, when Ijaws attacked oil facilities to protest what they said was the government's plan to redraw electoral districts to the Ijaws' disadvantage.
Ijaws clashed with government soldiers and later with members of a rival ethnic group, the Itsekeri, whom some Ijaws accuse of trying to monopolize political power in the region.
The government of President Olusegun Obasanjo, who is up for reelection next month, dispatched hundreds of troops to quell the violence.
On Tuesday, soldiers set up roadblocks to prevent militants from entering the oil producing areas around the southern city of Warri. Navy patrol boats were also blocking access via the area's swamps.
Nigeria is the world's sixth largest producer of oil. The shutdown of facilities caused by the unrest has cut production by a third, raising fears that world oil prices, already high due to the war in Iraq, may continue to climb.
It is also causing concern about stability in the country in the run-up to general elections scheduled for next month.