The US' decision to proceed with tariffs on aluminium and steel imports from Canada, Mexico and the European Union, causing dismay and anger among some of its top allies.
The European Union will impose counter measures, the head of the bloc's executive Jean-Claude Juncker said on Thursday.
"This is a bad day for world trade," Juncker said in a speech in Brussels. "So we will immediately introduce a settlement dispute with the WTO and will announce counter balancing measures in the coming hours.
"It is totally unacceptable that a country is imposing unilateral measures when it comes to world trade."
"We will have no choice but to defend European industry, jobs and interests. We will not accept this highly regrettable decision without reacting," Manfred Weber, an ally of German Chancellor Angela Merkel, said on Twitter.
Britain said it was deeply disappointed by the decision.
"The UK and other European Union countries are close allies of the US and should be permanently and fully exempted from the American measures on steel and aluminium."
US Commerce Secretary Wilbur Ross told reporters on Thursday in a telephone briefing that a 25 per cent tariff on steel imports and a 10 per cent tariff on aluminium imports from the EU, Canada and Mexico would go into effect at midnight Washington DC time on Friday.
"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," he said.
Ross offered little detail about what the EU, Canada and Mexico could do to have the tariffs lifted.