Gunmen have seized 15 children who were on their way to their international school in the south-eastern Nigerian state of Abia, say police. "The abductors have contacted [the owner of the private school] and asked for 20 million naira [$130,000; £81,500]," police spokesman Geoffrey Ogbonna told AFP news agency. He said he believed the children came from wealthy Nigerian families. The kidnap happened on the fringes of the oil-rich Niger Delta on Monday.