US President Donald Trump has said he is recommending a 50% tariff on all goods from the European Union being imported to the United States.

"Our discussions with them are going nowhere!" he wrote in a post on social media on Friday. He said the new tariffs would kick in on 1 June.

The announcement marks an escalation of Trump's trade war with the EU. He initially proposed a 20% tariff on most EU goods, but halved it to 10% until 8 July to allow time for talks.

The president also threatened to impose a 25% import tax "at least" on iPhones not manufactured in America.

"I have long ago informed Tim Cook of Apple that I expect their iPhone's that will be sold in the United States of America will be manufactured and built in the United States, not India, or anyplace else," Trump said.

"If that is not the case, a Tariff of at least 25% must be paid by Apple to the U.S."

Analysts said it remained to be seen whether the threats would turn into reality.

A tariff is a domestic tax levied on goods as they enter a country, proportional to the value of the import and it is paid by the business importing them.

Since re-entering the White House, Trump has imposed and threatened various tariffs on goods from countries around the world, which he sees as a way of boosting US manufacturing and protecting jobs from foreign competition.

The prospect of higher tariffs being introduced on imports to the US has rattled many world leaders because it will make it more expensive and difficult for businesses to sell goods in the world's largest economy.

The EU has not commented on the latest threat, which came just ahead of trade talks scheduled between the two sides.

Trade expert Aslak Berg from the Centre for European Reform said he thought Trump's post was intended to increase leverage.

"We have to keep in mind that at this point, this is a threat. It's not an announcement. There is no executive order," he said.

"But the fact of the matter is the EU is not going to budge. They are going to stay calm, carry on and it will be a very difficult discussion this afternoon."

Shares in the US and EU fell on Friday after the threats, with the S&P 500 down about 1% and Germany's Dax falling more than 1.7%.

Shares in Apple, which had won relief last month when Trump exempted key electronics including smartphones from his tariffs, opened more than 2% lower.

Trump has said he wants to reduce his country's longstanding trade deficit with the EU, which occurs when a country imports more than it exports. He blames the deficit on policies that he says are unfair to American companies.

On Friday, Trump said the EU had been "very difficult to deal with" and that the bloc had been formed "for the primary purpose of taking advantage" of the United States on trade.

"Our discussions with them are going nowhere! Therefore, I am recommending a straight 50% Tariff on the European Union, starting on June 1, 2025," he added.

Trump said there would be no tariff charged if the product was "built or manufactured in the United States".

Trump has repeatedly complained about the EU's car exports, particularly from Germany, to the US, with fewer vehicles being shipped the other way.

The boss of carmaker Volvo said in response to Trump's threat that customers would have to pay a large part of the cost increases resulting from tariffs.

Hakan Samuelsson told Reuters that a 50% tariff would limit the ability of the company to sell its Belgium-made EX30 electric vehicle across the Atlantic.

But he said he believed there would be a deal soon. "It could not be in the interest of Europe or the US to shut down trade between them," he said.

While some higher tariffs have been paused by Trump, foreign-made cars have faced a 25% levy since April.

Trump's warning to Apple comes after the tech giant said it was shifting production of most of its iPhones and other devices destined to be sold in the US away from China.

Apple chief executive Tim Cook said earlier this month that the majority of the iPhones bound for the US market in the coming months are to be made in India, while Vietnam will be a major production hub for items like iPads and Apple Watches.