Two American and two Canadian citizens have been freed after being kidnapped in the northern Nigerian state of Kaduna, a police spokesman said, as it emerged that five oil workers had been abducted in the southern Niger Delta region (pictured). Kidnapped Americans and Canadians have been rescued in Nigeria, police say https://t.co/nJKVqJssvH pic.twitter.com/xD4zd2Y7IW — CNN…