Earlier on Friday the EU's trade chief said the bloc expects to be excluded from US steel and aluminium tariffs but will go to the World Trade Organization to impose its own measures if Washington presses ahead.
EU President Donald Tusk yesterday warned Trump that "trade wars are bad and easy to lose", directly rebuffing the United States leader's claim last week they were "good and easy to win".
Trump last week he said his government would levy penalties of 25 percent on imported steel and 10 percent on aluminum imports, but left it unclear whether trading partners such as the European Union and Canada would be exempt.
Fragkiskos Filippaios, of the University of Kent's business school in England, says that the damage from a trade dispute will depend on whether the sides try to resolve their differences through the arbitration of the WTO, whose verdicts have so far always been accepted.
This increases political pressure on US President Donald Trump to give up his intentions to introduce duties on imported steel and aluminum.
The European Union and Japan, the United States' top economic and military ally in Asia, also reiterated that their exports were not a threat to USA national security, rejecting Trump's justification for imposing the tariffs.
After meetings with US trade envoy Robert Lighthizer in Brussels, EU and Japanese trade officials said negotiations would need to continue. "However, it is our goal to avoid a trade war".
EU Trade Commissioner Cecilia Malmstroem said Wednesday that the EU is circulating among member states a list of US goods to target with tariffs so that it can respond as quickly as possible.
"We are an ally, not a threat", Katainen said.
European Commissioner Malmstrom, who coordinates policy for the 28-nation EU, the world's biggest trading bloc, said she stood ready to go to the WTO, the global trade arbiter, to impose the bloc's own safeguards within 90 days.
The EU intends to hit a range of USA goods with punitive tariffs in retaliation should the bloc face the US import taxes. "We will have to protect our industry with rebalancing measures, safeguard", she added when asked if she would consider taking the dispute to the worldwide trade regulator.
Brazil, which after Canada is the biggest steel supplier to the U.S. market, said it wanted to join the exemption list and Argentina made a similar case.
The EU executive said it remained unclear how an exclusion would work.
The European Steel Association condemned Trump's decision, warning that it "could cost tens of thousands of jobs in the EU steel industry and related sectors".
The European Union, the world's biggest trade bloc, chimed in.
Commission Vice President Jyrki Katainen warned Washington on Friday not to expect any concessions to win an exemption.