BERLIN (Reuters) - Germany has decided in principle to purchase the U.S. fighter jet F-35 built by Lockheed Martin to replace its ageing Tornado, according to two government sources.

       A German defence source told Reuters in early February that Germany was leaning toward purchasing the F-35 but a final decision had not been taken.

       The Tornado is the only German jet capable of carrying U.S. nuclear bombs, stored in Germany, in case of a conflict. But the air force has been flying the jet since the 1980s, and Berlin is planning to phase it out between 2025 and 2030.

       It was not clear how many F-35 jets Germany may attempt to purchase.

       The F-35 buy will be a blow for Boeing, whose F-18 was favoured by former German defence minister Annegret Kramp-Karrenbauer to replace the Tornado.

       The decision to go with a U.S. fighter jet could also upset France. Paris has been warily watching past German deliberations over whether to settle on the F-18 or the F-35, concerned it could undermine the development of a joint Franco-German fighter jet that is supposed to be ready in the 2040s.

       (Reporting by Andreas Rinke, Sabine Siebold; Writing by Miranda Murray; Editing by Kirsti Knolle)