N'DJAMENA, March 23 (Reuters) - Chad has nationalized all the assets and rights including hydrocarbon permits and exploration and production authorisations that belonged to a subsidiary of Exxon Mobil (XOM.N), the Central African nation's energy and hydrocarbons ministry said in a statement on Thursday. Exxon Mobil said in December that it had closed the sale of its operations Chad and Cameroon to London-listed Savannah Energy (SAVES.L) in a $407 million deal, but the Chadian government contested the agreement, saying the final terms were different from what Exxon Mobil had presented. It warned that it may ask courts to block Savannah's...