BRUSSELS—The European Union and Japan pressed the U.S. to exempt them from President Donald Trump’s steel and aluminum tariffs on Saturday, as officials seek to avoid a trade war with the world’s biggest economy.

U.S. Trade Representative Robert Lighthizer met with EU Trade Commissioner Cecilia Malmstrom and their Japanese counterpart, Hiroshige Seko, in Brussels as part of a trilateral effort to combat unfair trade practices.

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