The move, announced by US Commerce Secretary Wilbur Ross in a telephone briefing on Thursday, ended months of uncertainty about potential tariff exemptions and suggested a hardening of the Trump administration's approach to trade negotiations.
"They don't quite understand this is going to harm Americans" as well, he said.
The news pushed markets - already jittery as a result of the political chaos in Italy and Spain - into negative territory.
The S&P 500's packaged foods and meats industry sub-index fell 2.4 percent, with shares of meat producer Tyson Foods Inc dropping 4 percent.
The problems of steel dumping will not be solved by unfair tariffs, and steelworkers in the United Kingdom and U.S. must not fall into the trap of believing rhetoric from the likes of Donald Trump.
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Both the ISIS affiliate and the Taliban have launched several attacks in Kabul in recent months, killing hundreds of people. ISIS claimed responsibility for the attack a few hours later in a statement released by ISIS' media wing, Amaq Agency.
U.S. stocks shuddered at the news, however, with the The Dow Jones Industrial Average dipping over one percent, S&P 500 dropping 0.54 percent, and the Nasdaq going down 0.16 percent.
- While a trade war with China may be on hold, the European Union seems poised to retaliate against the USA measures.
In response, European Union chief Juncker said the U.S. tariffs decision leaves the bloc with "no choice" but to impose counter-measures and pursue a case in the World Trade Organisation. "We should build on our success in overhauling the nation's tax code with complementary trade policies that, rather than favoring one narrow industry, make all sectors of the USA economy more competitive".
"If any of these parties does retaliate, that does not mean that there can not be continuing negotiations", Ross said.
"By targeting those who are not responsible for overcapacities, the U.S.is playing into the hands of those who are responsible for the problem", he said. USA leaves us no choice but to proceed with a WTO dispute settlement case and the imposition of additional duties on a number of U.S. imports.
Trump invoked a 1962 trade law to erect protections for USA steel and aluminium producers on national security grounds, amid a worldwide glut of both metals that is largely blamed on excess production in China.
"We had discussions with the European Commission and while we made some progress, they also did not get to the point where it was warranted either to continue the temporary exemption or have a permanent exemption", Ross said. We did everything to avoid this outcome. "This doesn't bode well for NAFTA negotiations".
European Union declares dark day for trade as Trump slaps steel tariffs
Wilbur Ross , the commerce secretary, broke the news on a call with reporters Thursday morning. South Korea has not negotiated an exemption for its aluminum exports.
"It's not everyone attacking the other and we see who remains standing at the end", he said, declaring that the stiff U.S. duties were "unjustified, unjustifiable and unsafe".
In a trade war it can be hard to tell friends from enemies.
But the tariffs stung particularly in Canada, where Trudeau evoked the history of two countries fighting together from the beaches of Normandy to the mountains of Afghanistan.
The EU said on Thursday it will impose retaliatory duties, a measure the bloc earlier indicated would target US$3.3 billion in American products from Harley-Davidson Inc. motorcycles to Levi Strauss & Co.'s jeans as well as bourbon whiskey. The legality of that policy would once again rest on the president's authority to protect national security through unilateral trade actions (ostensibly, one can never be too sure that Angela Merkel isn't about to conquer the United States with a fleet of autonomous BMWs). It is only right that have been rebuffed by European Commissioner, Cecilia Malmström. Nucor Corp., the biggest USA steel producer, rose 0.6 per cent to US$64.49.
The global response to the action was swift.
Ben Digby, the worldwide director of the Confederation of British Industry, added: "The President's measures are deeply concerning for firms in the United Kingdom, for close trading partners and across supply chains".
"Now is not the time for any disproportionate escalation, and we urge the European Union to consider this when initiating its response", he added.
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Yet after North Korea agreed to the summit, those intentions were thrown into doubt when Pyongyang rejected calls from U.S. Trump's "maximum pressure" campaign has led global efforts to impose sanctions banning 90 percent of the North's trade.