Gunmen in Nigeria's oil region have attacked and killed 12 people including four local chiefs, police say.
Unrest in the Delta cost $4bn last year
Two passengers who suffered gunshot wounds during the attack escaped from a boat that was carrying 14 passengers to Kula village in the Niger Delta.
The four chiefs were from the Kula kingdom in Rivers State.
Western oil companies have also evacuated their staff from three oil fields in the area, where kidnappings by armed groups are quite common.
Sources in the Kula community say the attack was prompted by disagreements between local groups over sharing out money distributed by oil companies operating there.
There are also reports that the attack could have been a result of a long-standing chieftaincy tussle.
The chiefs who were killed on Sunday had been in control in Kula over the past two years.
The faction that launched the boat attack are said to have been driven out of Kula two years ago after they challenged the authority of local chiefs to share oil money.
Although all of Nigeria's oil exports come from the Niger Delta, the region remains poor with local groups taking up arms to demand larger control of the oil wealth.
The government says instability in the Delta cost some $4.4bn last year.