TOKYO—Prime Minister Shinzo Abe offered a stout defense of the U.S.-Japan alliance and warned against “naked nationalism” amid an American presidential campaign in which the countries’ longtime security ties have been called into question.

Mr. Abe also told The Wall Street Journal in an hourlong interview Tuesday that the U.S. and other wealthy nations should uphold existing trade deals, and said he wanted to push through a Pacific trade agreement that presidential candidates of both parties have called a bad deal for America.

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