 President Mohammed Buhari says the deaths of the chief of army staff, Lieutenant General Ibrahim Atehrou, and 10 other military officers have increased Nigeria's security challenge. The president regretted that the bad incident occurred at the time the country's battling security challenges. Buhari spoke on Monday when he received a delegation from the Nigeria Governor's Forum who came to the president to Vila Abuja to condone with him on Friday's air crash that occurred in Kaduna.