The Trump administration has announced plans to impose tariffs on some metal imports from the EU, Canada and Mexico from midnight tonight.
The US Commerce Secretary Wilbur Ross confirmed there will be a 25% on imported steel and 10% on aluminium.
The administration has cited 'national security' concerns for the move.
This afternoon, the EU pledged to target a number of US products with retaliatory tariffs - as well as saying it would launch legal proceedings against the US through the World Trade Organisation.
The Trump administration originally announced the aluminum and steel tariffs in March, prompting fears of a trade war.
Officials ultimately granted exemptions to a number of close allies to allow for negotiations, but officials now say not enough progress has been made in talks.
However, the White House says a 'range of measures' have been agreed with Argentina, Australia, Brazil and South Korean - meaning they will be able to avoid some of the new tariffs.
Mr Ross said: "We look forward to continued negotiations, both with Canada and Mexico on the one hand, and with the European Commission on the other hand, because there are other issues that we also need to get resolved."
EU reaction
Antonio Tajani, President of the European Parliament, said he was 'very disappointed' by President Trump's response - and pledged the EU 'will respond with all available tools to defend our interests'.
I am very disappointed by President Trump's decision to impose duties on EU steel and aluminium imports. We stand by our European workers and industry and will respond with all available tools to defend our interests. Unilateral trade tariffs are always a negative sum game.
— Antonio Tajani (@EP_President) May 31, 2018
Jean-Claude Juncker, President of the European Commission, also said he was concerned with the move.
He said: "Over the past months we have continuously engaged with the US at all possible levels to jointly address the problem of overcapacity in the steel sector. Overcapacity remains at the heart of the problem and the EU is not the source of but on the contrary equally hurt by it.
"By targeting those who are not responsible for overcapacities, the US is playing into the hands of those who are responsible for the problem. The US now leaves us with no choice but to proceed with a WTO dispute settlement case and with the imposition of additional duties on a number of imports from the US."
US products such as Kentucky bourbon and Harley-Davidson motorcycles are now likely to be hit with additional duties.