Europe and Mexico pledged to retaliate quickly, exacerbating trans-Atlantic and North American trade tensions.
Speaking to an energy conference in Brussels as the United States decision was announced, Jean-Claude Juncker urged... "This is protectionism, pure and simple".
"If there is an escalation it will be because the European Union would have made a decision to retaliate", he said, adding that Washington did not want a trade war with the EU.
While not confirming directly that the USA would decide to impose tariffs, he said: "It's up to the European Union to decide if it wants to take retaliatory measures".
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She urged the U.S. to keep its "word and work" with China according to the spirit demonstrated in the joint announcement. But just over a week ago Treasury Secretary Steven Mnuchin had said a trade war with China was " on hold ".
The organisation's director Gareth Stace said: "US steel consumers are already reporting price increases and supply chain disruption and with $500m of steel exported from the United Kingdom to the USA past year, United Kingdom steel producers are going to be hit hard".
The move, which President Trump has threatened for months, is likely to provoke retaliation from the European Union, which has pledged to counter with tariffs on American staples including Harley-Davidson motorcycles, Levi's jeans and bourbon whiskey.
Wilbur Ross, the commerce secretary, broke the news on a call with reporters Thursday morning.
Trudeau and French President Emmanuel Macron made their cases separately Wednesday to dissuade Trump, who is using a national-security clause in US trade law to justify the move.
"Today is a bad day for world trade", said Cecilia Malmström, the European trade commissioner.
And despite the picking and choosing of which allies that the USA decides to slap with these tariffs, Ross defended the US legal justification that they are being implemented under law meant to protect USA national security.
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Kim Yong Chol is a vice chairman of the North Korean ruling party's central committee. Reported by Myungchul Lee for RFA's Korean Service.
"Throughout these talks, the U.S. has sought to use the threat of trade restrictions as leverage to obtain concessions from the EU". There's little logic in imposing tariffs on metal imports from the Nafta partners.
Ross says there remains some flexibility and he is looking forward to continuing negotiations.
Molson Coors analyst Brittany Weissman of Edward Jones says brewers will try to pass along the higher costs to consumers but the industry's current demand challenges may make that hard. "We will respond appropriately". Yet Canada is also, far and away, the largest export market for US steelmakers.
The bloc's response will be "united and firm", French Finance Minister Bruno Le Maire warned.
"This will only lead to the victory of those who want less growth, those who don't think we can develop our economies across the world".
The three allies lambasted the U.S. decision, calling the move a violation of trade rules and a breakdown of worldwide cooperation. "We are ready to rebuild this multilateralism with our American friends", he said. "We did everything to avoid this outcome".
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