Ijaw militants want more political power and oil money
At least 12,000 people have fled their homes following clashes in and around the southern oil town of Warri, according to the Nigerian Red Cross.
"These are people who were either made homeless because their houses have been burnt or were forced to flee the conflict area," Emmanuel Ijewere, president of the organisation said.
Reports say several people have been killed, scores more injured and property looted and burned in the fighting, which is both political and ethnic.
Tensions heightened in the Nigerian Delta during last month's disputed presidential and state governor elections - and are rising again ahead of local polls on 21 June.
The BBC's Robert Efenakpo in Warri says that he saw three bodies in the village of Effurun, 2 kilometres from Warri.
An army officer said that at least 13 people have been killed in clashes between supporters of the opposition Alliance for Democracy (AD) and activists from the ruling People's Democratic Party (PDP).
Our correspondent says that the army has now been deployed to Effurun but the situation is tense.
On Tuesday, ethnic Ijaw leaders called for an end to the recent violence, which has often seen Ijaw youths pitted against Itsekeri rivals or the army.
"After due consultations with all leaders of opinion it has been agreed that peace should be allowed to reign in Warri and environs," said a statement released by Ijaw leaders in Warri and signed by their leader, Chief Edwin Clark, reports Reuters news agency.
A temporary ceasefire would be in place while the government worked out "a political solution that will satisfy the majority of ethnic groups and... bring permanent peace to the Warri areas," it said.
This call was aimed more at the ethnic violence than the political clashes, which began on Sunday morning.
Our correspondent says that a pregnant woman was killed by stray bullets in Effurun.
Her body was left
along with four others for several hours in the
scorching sun by the roadside on Tuesday.
Soldiers frequently battle Ijaw militants
Some petty traders and passers-by have been robbed by those taking advantage of the unrest.
Ijaws demand a greater share of local political power and more of the benefits of the region's oil.
Last month's general elections were marred by violence and fraud in Warri and the surrounding Delta State, observers said.