British Prime Minister Theresa May told President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in a call Monday that his decision to impose steel and aluminum tariffs on the European Union is “unjustified and deeply disappointing,” her office said.

“The prime minister raised the U.S. decision to apply tariffs to EU steel and aluminum imports, which she said was unjustified and deeply disappointing,” a Downing Street spokesperson said.

May's office said she stressed that "the U.S., U.K. and EU are close national security allies and we recognize the importance of the values of open and fair trade across the world.”

The White House said later Monday that Trump “underscored the need to rebalance trade with Europe” during his call with May.

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The two leaders agreed to discuss the matter further at the Group of Seven summit of world economic powers in Canada this weekend, according to the British government. They are also scheduled to meet in July when Trump travels to Great Britain.

Trump’s decision to impose steel and aluminum tariffs on European and North American nations outraged U.S. allies and raised fears of a global trade war.

Canada, Mexico and the E.U. have said they would retaliate with their own tariffs on U.S. goods and pledged to bring a case before the World Trade Organization.

At the same time, the Trump administration is considering slapping tariffs on $150 billion in Chinese goods in response to what the U.S. says is Beijing’s forced technology transfers on U.S. companies seeking to do business there.

Trump defended his move in a series of early morning tweets.

“The U.S. has made such bad trade deals over so many years that we can only win!” he wrote.

--Updated at 2 p.m.