The governor of Nigeria's Kaduna state has been killed in a helicopter crash in the southern delta region along with other senior officials, his party says.Governor Patrick Ibrahim Yakowa and former national security adviser Gen Owoye Azazi were on the helicopter which came down in Bayelsa state.Nigerian media said the helicopter belonged to the Nigerian navy and had been taking officials to Port Harcourt.Nigeria has a poor air safety record, analysts say.In March a police helicopter carrying a high-ranking police official crashed in the central city of Jos, killing four people."The nation has lost a great patriot who in about two years in saddle as the Governor of Kaduna State demonstrated an unyielding capacity in wielding together varying fragile interests," the Peoples Democratic Party said in a statement.Kaduna, in northern Nigeria, is a volatile region with a mixed population of Muslims and Christians. The Islamist militants of Boko Haram have frequently targeted Kaduna churches.