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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, 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 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 purchase of Exxon's assets in the country and take further steps to protect its interests.

Exxon's assets included a 40% stake in Chad's Doba oil project, which comprises seven producing oilfields with combined output of 28,000 barrels per day (bpd).

It also included Exxon's interest in the more than 1,000 kilometre (621 mile) Chad/Cameroon pipeline from the landlocked nation to the Atlantic Gulf of Guinea coast through which its crude is exported.

Exxon Mobil and Savannah Energy were not immediately available for comment. (Reporting by Mahamat Ramadane; Writing by Bate Felix; Editing by Cynthia Osterman)