"We cannot allow this country to be overtaken by hoodlums and criminals. When people decide to behave like animals they must be treated like animals," Obasanjo said on state television.

Rioting erupted between ethnic Hausas and militant Yorubas from the Oodua Peoples Congress (OPC) in the Ketu Suburb and continued even after paramilitary police intervened to separate the two sides.

"The police have instructed that any criminal should be shot on sight," Obasanjo said.