Good background on the riots from Al Jazeera English

Al Jazeera English - Africa - Clashes near Nigerian city of Jos

Charles Dokubo, from the Nigerian Institute of International Affairs, told Al Jazeera: "There is more than the religious aspect of it. There are two communities - one that call themselves settlers and one that call themselves indigenous communities.

"The crisis in the north started with the creation a local government."

Dokubo said that Muslim settlers were to manage the government, which was unacceptable to the indigenous Christian community who consider them non-citizens.

"The main cause of the crisis is about administration and the place where people belong."

The only correction I would add is that the indigenes don't consider them non-citizens, rather they consider them strangers or guests (same concept in Africa) and they believe they should have the rights of guests, not of indigenous people, or "sons of the soil" in African terms.