“In terms of uncertainty we’re back to where we were last year,” he told the BBC’s Today programme, adding there was now a higher risk that the US’s trading partners would retaliate.
“The risk of a real fully-fledged tariff war – trade war – escalation is clearly higher than last year,” he said.
The executive order, external signed by Trump on Friday said the temporary import duty was intended to “address fundamental international payments problems and continue the Administration’s work to rebalance our trade relationships to benefit American workers, farmers, and manufacturers”.
The administration is applying the levy under Section 122 of the 1974 Trade Act, external, which allows the president to impose the charge for 150 days without congressional approval.
The president has argued that tariffs are necessary to reduce America’s trade deficit – the amount by which imports exceed exports. But the deficit reached a fresh high last week, widening by 2.1% compared to 2024 and hitting roughly $1.2 trillion (£890bn).
The US has already collected at least $130bn in tariffs using the 1977 International Emergency Economic Powers Act (IEEPA), according to the most recent official data.
Trump has been highly critical of the Supreme Court’s decision, calling it “ridiculous, poorly written, and extraordinarily anti-American”.
In a 6-3 decision, justices on the highest US court found that the president had overstepped his powers when he introduced sweeping global tariffs last year using the IEEPA.
On Monday, Trump threatened to impose higher tariffs on countries that “play games” with recent trade deals, after the Supreme Court ruling.
His warning came as countries around the world said they were evaluating what tariffs and trade deals would stand following the decision.
The UK said no reciprocal action was “off the table” if the US did not honour its tariff deal with the UK, but added that “no one wants a trade war”.
The European Union said it would suspend its ratification of a deal struck over the summer.
“If we get worse conditions then we need to react,” said the chair of the European Parliament’s delegations for relations with the US, Brando Benifei, adding that the EU had asked the US for clarity over the tariffs
“I think you should demand respect,” he told the Today programme. “My plea is that all the countries in the world that do not like that we are being treated this way… try to work a bit together.”
India also said it would defer previously scheduled talks to finalise a recent agreement.