Dozens of shops and cars are said to have been destroyed in the riot, which shook the south-western city on Friday.

The clash between cattle ranchers and market traders is said to have started when traders found that a rancher had been released by police after he allegedly killed a trader in a dispute over a goat.

Newspapers say the riot was between ethnic Yoruba traders and Hausa cattle dealers - Nigeria's two largest ethnic groups. The Yorubas make up most of Ibadan's population.

"When the traders learnt of the death of the young man they went to inform the police but became furious upon the information that the Hausa man had since been released," the independent Guardian newspaper said.

Ethnic hostility

The dispute appears to have taken on an ethnic character as war songs were sung, and traders and ranchers began attacking one another.

The violence continued for several hours. Over 100 shops are reported to have been burnt. Cars which had been abandoned by their owners were also set alight.

Riot police were called out, and at least 10 people arrested.

Delta ceasefire

The Delta has a complex ethnic make up

The Ibadan riot happened as three feuding ethnic groups in the troubled Delta region agreed to cease hostilities to make way for peace negotiations.

The agreement between the Ijaws, Itsekeris and Urhobos was reached at talks under the supervision of State Governor James Ibori.