By Barnaby Phillips in Lagos

Reports from the south-western Nigerian city of Ibadan say that several people have been killed in ethnic clashes involving the Yoruba and Hausa people.

The violence is reported to have begun when a truck driven by a Hausa man collided with a taxi carrying several Yorubas.

Some reports said seven people were killed in the crash, whilst four others died in subsequent fighting. Houses were set on fire before the police restored order.

In the Lagos slum area of Mushin, senior police commanders said that they had restored order after violence that they blamed on the extremist Yoruba organisation, the Odua People's Congress (OPC).

The fighting in Mushin is reported to have resulted in at least 10 deaths.

One police commander told the BBC that the OPC had been attempting to drive armed robbers out of Mushin, which is a notoriously violent part of the city.

Rising tide of violence

The police have accused the OPC of involvement in a series of bloody incidents in and around Lagos in recent weeks.

The OPC denies it is encouraging ethnic clashes, but it is outspoken in its defence of the rights of the Yoruba people, who are the majority in south-western Nigeria.

President Olusegun Obasanjo, who leads the democratic government that took over from the military last May, is trying to control a rising tide of ethnic chauvinism.

There have been numerous ethnic clashes in Nigeria in recent months.

In November, some 100 people were killed in Lagos during fighting between the Yorubas and Hausas, who are the two largest ethnic groups in the country.