The European Union's trade chief questioned Wednesday U.S. President Donald Trump's rationale in proposing steel and aluminum import tariffs on a longstanding ally and said his move undermined trans-Atlantic ties ever more.

Trade Commissioner Cecilia Malmstrom told the EU legislature Wednesday that while the 28-nation EU would continue to seek exemption from the U.S. measure that could kick in next week, it will prepare countermeasures to hit U.S. exports.

Malmstrom also objected to Trump's claim that the tariffs are needed to protect national security since most EU nations are allied with the United States in the defense and security NATO alliance.

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