Nigeria's police minister has called for calm after attacks in the oil-rich Delta region at the weekend left at least 10 dead and dozens of homes burnt.
Ijaw militants have taken hostages to press their claim for more oil wealth
Chief Broderick Bozimo said the traditional rulers of the Ijaw and Itsekiri ethnic groups were not doing enough to put an end to the inter-ethnic hostilities.
The attacks on three Ijaw villages followed reports that an Itsekiri village was attacked last week, resulting in the deaths of at least 15 people.
Bloody clashes between the two groups over political power and land rights in the past few years have claimed hundreds of lives and made thousands more homeless.
An Ijaw representative, who wished to remain anonymous, told Reuters news agency: "The situation is very tense, because the Ijaw people will definitely retaliate."
The Ijaw group in particular want more of the benefits of the region's oil.
During the election campaign earlier this year, violence led to several multinationals pulling their staff out of the poverty stricken Delta and led to Nigeria's crude oil exports to be cut by 40%.
The elections themselves were marred by violence and fraud in Warri and the surrounding Delta State, observers said.
The violence now appears to be escalating again.
Delta State governor James Ibori summoned Ijaw and Itsekiri representatives for talks on Monday afternoon.