BRUSSELS (AP) — The European Union's trade chief questioned on 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 on 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.

Trump has said that the tariffs are necessary on national security grounds, but Malmstrom insisted this is a ruse: "We suspect that the U.S. move is effectively not based on security considerations but an economic safeguard measure in disguise."

Increasing mistrust between the long-time allies has increased since Trump became president last year, but seeking to hurt the EU economy with tariffs has acerbated ill feelings. It was evident in the EU legislature in Strasbourg, France, where parties of just about all persuasions lined up to criticize the U.S. plans.

The EU says that rather than impose tariffs on friendly nations, the U.S. should cooperate in trying to reduce a glut of steel and aluminum on international markets, which experts says is largely due to China's overproduction in recent years.

"That is what makes the sound bites of the current US administration so disturbing," said Marietje Schaake of the parliament's ALDE liberal group. "Right at the time we need to work together as the liberal democracies of this world to curb unfair trade practices of China and others, we are divided."

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.

"We are very disappointed indeed that longstanding allies and security partners from Europe need to justify their exports of steel and aluminum and to prove that they are not a threat to U.S. security."