Nigerian President Goodluck Jonathan on Thursday appointed a new defense chief for the West African country, urging him to work hard to strengthen and preserve the national integrity. The new defense chief, Vice Admiral Ola Ibrahim, takes over from Air Chief Marshal Oluseyi Petinrin who retired from office. He had served as chief of naval staff until his new appointment by the Nigerian president. \"We hope the new chief of defense staff would continue to work hard in his service to the nation,\" said a statement released by the presidency. Nigeria\'s incumbent army chief Lt.-Gen. Azubike Ihejirika retains his position. The Nigerian president also appointed the naval chief and chief of air staff. \"President Jonathan thanked the outgoing service chief for his meritorious and commendable service to the nation and wishes him well in his future endeavors,\" the statement added.