Donald Trump unveiled plans to step up his trade wars on Monday, announcing Japan and South Korea will soon face US tariffs of 25% in a significant escalation of his controversial economic strategy.

The US president, who indicated that he would notify as many as as 15 countries of new, higher rates on Monday, posted copies of letters addressed to the leaders of Japan and South Korea on social media. Trump said the rates were set to go into effect 1 August.

The letters were largely identical and informed the leaders that there will be no tariffs if their countries “decide to build or manufacture product within the United States”.

Trump also threatened higher tariffs if the countries place additional tariffs on US exports. “If for any reason you decide to raise your tariffs, then, whatever the number you choose to raise them by, will be added onto that 25% we charge,” he wrote.

Trump initially announced a slate of so-called reciprocal tariffs in April, on what the White House dubbed “liberation day”, with some countries facing rates as high as 50%

While he paused those tariffs for 90 days amid market turmoil, this reprieve is due to expire on Wednesday 9 July.

Trump officials initially suggested they would strike dozens of deals with key economies during the pause, but have since indicated that they would use an extension to continue talks.

The treasury secretary, Scott Bessent, said last month the administration was aiming to wrap up negotiations by Labor Day on 1 September.

The US has so far settled deals with three countries: the UK, China and Vietnam, and Bessent said there were over a dozen countries the US is still trying to negotiate with.

The new August deadline for countries without a deal amounts to a further three-week reprieve, but also triggers fresh uncertainty for importers because of the lack of clarity around the tariffs.

As the July deadline has approached, Trump’s officials have been racing to broker deals. Over the weekend, one European diplomat said the US may have to “show muscle if the deal is not good enough”.

The White House also reached an impasse in negotiations with Japan, despite initial optimism. Trump on Friday said it is “much easier to send a letter” and that the offers are “take it or leave it”.

On Wall Street, the benchmark S&P 500 sank by almost 0.9% after Trump posted his first letters.

Though the US stock market has largely recovered from the uncertainty around Trump’s trade war, the US dollar still remains weakened after months of trade fights. At the beginning of this year, the dollar had its worst six months in over 50 years, falling 10.8% since the start of 2025.

The US plans to impose a 25% tax on products entering the country from South Korea and Japan on 1 August, President Donald Trump has said.

He announced the tariffs in a post on social media, sharing letters he said had been sent to leaders of the two countries.

The White House has said it expects to send similar messages to dozens of countries in coming days as the 90-day pause it placed on some of its most aggressive tariffs is set to expire.

The first two letters suggest that Trump remains committed to his initial push for tariffs, with little change from the rates announced in April.

At that time, he said he was looking to hit goods from Japan with duties of 24% and charge a 25% on products made in South Korea.

Those tariffs were included in a bigger “Liberation Day” announcement, which imposed tariffs on goods from countries around the world.

After outcry and turmoil on financial markets following the initial tariffs announcement, Trump suspended some of the import taxes to allow for talks. That deadline is set to expire on 9 July.

On Monday, Treasury Secretary Scott Bessent said he expected “a busy couple of days”.

“We’ve had a lot of people change their tune in terms of negotiations. So my mailbox was full last night with a lot of new offers, a lot of new proposals,” he told US business broadcaster CNBC.

Labour’s most high-profile billionaire backer, who switched allegiance from the Conservatives, has said he is “increasingly nervous” about the government’s direction and is in “despair of politicians”.

John Caudwell, the Phones 4u founder, said Labour’s winter fuel payments cut was a “fiasco” and ministers were not doing nearly enough to attract investment into the UK.

Caudwell, who has pledged to give away more than 70% of his £1.58bn fortune, said a wealth tax would be “very destructive” to growth.

The businessman – a prominent Brexit supporter who backed the Conservative party for many years – said he could never support Nigel Farage’s Reform UK because he was convinced of the need to tackle the climate crisis and urged Labour to be bolder on net zero.

Caudwell was speaking at the launch of a report from his charity Caudwell Youth, urging more investment in early intervention in the lives of disadvantaged young people and a renewed focus on mental health.

He said despite his own background in mobile phones, he believed social media and AI were a “disaster” for anxiety and feared a world where AI fakes were the norm.

Caudwell said he welcomed some important changes from Labour, including to pension funds, planning changes and green energy, though he said schemes such as Great British Energy could go further and were “lacking in ambition”.

He said Labour had been poor at telling the right story and the winter fuel saga and the welfare rebellion had been unnerving. “They’re just going to be tossed from pillar to post, that’s how it feels,” he said.

“I am becoming increasingly nervous about what Labour are doing and especially when they get into this mess over the welfare bill because it feels as though there’s anarchy within the party.”

Caudwell said he had repeatedly offered advice to Keir Starmer and Rachel Reeves, but had not received much interest in his ideas. “There seems to be a lack of that commercial intellect that we desperately need in government to make long-term right decisions,” he said.

He said he knew many wealthy individuals and business owners moving to Dubai or Monaco, and that the UK needed to become a more attractive place to invest.

“I despair of politicians in general,” Caudwell said. “You’ve got to attract inward investment to create high-paid jobs and in technology, sciences and especially in the environment, since that’s going to be the absolute future of mankind.

“There’s so much we need to do and there’s so little we do, and that was the Conservative party before and now it’s the Labour party.”

Caudwell said he did not regret switching his allegiance from the Conservatives, having previously donated £500,000 to them under Boris Johnson. “I don’t regret it. But do I regret some of the decisions they’ve made? Absolutely I do. And I think they could have done so much better.”

Senior Labour figures have suggested the party should introduce a wealth tax on rich people in the budget. The former Labour leader Neil Kinnock said on Sunday such a gesture “in the direction of equity fairness would make a big difference”.

But Caudwell said a wealth tax combined with other measures Labour had introduced would be a major disincentive for investors, even if he would personally be happy to pay.

“I would be very in favour of a wealth tax if it was global,” he said. “The rich-poor divide is the evil of society and how do we fix that?”

But he said that changes to agricultural property relief, changes to workers’ rights and increases to the minimum wage and employers’ national insurance was creating a more difficult climate for business.

“I think you can do some of those things, but you just can’t do everything,” he said. “You introduce a wealth tax on top of that and it just isn’t going to work. I know people that are leaving as we speak. They’re going to Monaco, they’re going to Dubai.

“I bet 10 people in the last three or four months have said, ‘Why don’t you go to Dubai?’ Well, I don’t want to go to Dubai, I’m British, I love it here. I don’t mind paying my taxes.

“I want to influence rich people to do more philanthropically and to pay taxes. A wealth tax would be very destructive on top. I don’t say that because I’m trying to protect my money – because I’m giving it away.”

Caudwell said Starmer should be bolder in his second year as prime minister. “I’d be a bit like a [version of] Trump who’s smart and who’s humanitarian. And I’d force things through. You wouldn’t do any of the same things [as Trump], but it is what we need.”

The businessman has previously been a guest of Farage on GB News and said the pair agreed on a lot of topics. But he ruled out backing Reform, calling Farage a “climate sceptic” and said the climate crisis was “the most crucial thing we’re facing”.

“I would be concerned that he’s too much of a Trumpite … and that would not be healthy for Britain at all. But a lot of what he says makes a lot of sense to me,” he said. “He’s able to talk very directly to people’s concerns.”

Caudwell said he would continue to urge a focus on young people and how investment in prevention would save billions in the long run for the justice system and the NHS.

“I think social media is disastrous for people’s mental health,” he said. “AI is going to be completely disastrous. Even up until probably four or five years ago, if I watched a video, I’d know it was real.

“Now the kids are going to see this stuff, they’re not going to have a clue what’s real. And I think that’s really worrying because our children are going to grow up in this fantasy world where they don’t know right from wrong, fact from fiction.”