Four people have been killed in gun battles between rival gangs in Port Harcourt, the main city in Nigeria's oil-rich Niger Delta region.
A large fuel-pumping station in the city was also attacked.
The latest violence brings the number killed in nearly a week of fighting between gangs to at least 10 people.
Violence around Port Harcourt has increased since militants launched a campaign last year for a greater share of oil revenue for the poor region.
Oil output cut
The fighting began on Monday with sporadic clashes between gangs that Port Harcourt residents say are vying for control of territory in the city.
Residents reported gunshots and explosions through Friday night and on Saturday the battles intensified.
Security forces have set up roadblocks and mounted patrols in some areas of the city.
The security situation in southern Nigeria's oil-producing region has deteriorated since early 2006 with attacks on oil installations and foreign workers kidnapped for ransom.
The main militant group, the Movement for the Emancipation of the Niger Delta (Mend), agreed to a ceasefire last month but recently threatened to resume attacks.
The unrest has led to a 25% cut in oil output from Nigeria - Africa's largest producer.
President Umaru Yar'Adua has said tackling the unrest in the south is one of his top priorities.