Gunmen in Nigeria have freed nearly 200 prisoners from a jail, a Nigeria Prison Service spokesperson has told the BBC.Hadijha Aminu said the jail in Koton-Karif town in the central state of Kogi was attacked on Wednesday evening.She said a large number of men with weapons stormed the prison, but details of the attack were still sketchy.But she said the authoritities did not believe it was the work of Boko Haram, the Islamist group behind a massive jailbreak in 2010 in Bauchi state.