The United States will double its tariffs on imported steel and aluminium starting Wednesday, according to the White House, which published an order signed by President Donald Trump.
The move marks the latest salvo in Trump's ongoing trade disputes, raising levies on both metals from 25 percent to 50 percent.
However, tariffs on metal imports from the United Kingdom will remain at the 25 percent rate, while both sides negotiate duties and quotas in line with the terms of a prior trade agreement.
Overall, the aim is to "more effectively counter foreign countries that continue to offload low-priced, excess steel and aluminium in the United States", the order said, adding that such imports undercut the competitiveness of domestic industries.
"Increasing the previously imposed tariffs will provide greater support to these industries and reduce or eliminate the national security threat posed by imports of steel and aluminium articles and their derivative articles," it added.
Trump first announced the decision during a speech at a US Steel plant in Pennsylvania last week.
"Nobody is going to be able to steal your industry," he said at the time. "At 25 percent, they can sort of get over that fence. At 50 percent, they can no longer get over the fence."
The move has escalated tensions with key trading partners. Over the weekend, the European Union warned it was prepared to retaliate if no agreement is reached.
Brussels said the sudden announcement "undermines ongoing efforts to reach a negotiated solution" between the bloc and Washington.
Washington is currently in talks with several countries after Trump imposed sweeping 10 percent tariffs in April on nearly all trade partners and announced even higher rates for dozens of economies.
While the steeper duties have been paused during ongoing negotiations, this halt is due to expire in early July, adding urgency to resolve outstanding trade issues.
Since returning to office in January, Trump has imposed wide-ranging tariffs on both allies and adversaries, shaking financial markets and prompting fears of a global trade war. In addition to metals, he has targeted sector-specific imports such as automobiles.
