Washington DC - President Donald Trump on Friday threatened Apple and other smartphone manufacturers with a 25% tariff unless their devices are built in the US.

Trump initially said the tariff would apply only to Apple – an unusual move to single out a specific company in trade policy. However, he later expanded the threat to include all smartphone makers.

"It would be also Samsung and anybody that makes that product, otherwise it wouldn't be fair," Trump told reporters in Washington, adding that the new tariffs would take effect by the "end of June."

While Apple designs its products in the US, most iPhone assembly occurs in China, which remains embroiled in a trade war with the US.

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Apple has announced plans to shift some production to other countries, including India, but Trump said this would not satisfy his demands.

In a post on Truth Social earlier Friday, Trump wrote that he had "long ago informed Tim Cook of Apple that I expect their iPhones that will be sold in the United States of America will be manufactured and built in the United States, not India, or anyplace else."

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

Trump's Friday comments echoed statements he made during a trip to Qatar last week, when he urged Apple to bring iPhone production to the US.

"I had a little problem with Tim Cook," Trump said on May 15.

He recounted how he told Apple's CEO, "We're not interested in you building in India... we want you to build here and they're going to be upping their production in the United States."