(Reuters) - U.S. President Donald Trump said on Friday that Apple would have to pay a 25% tariff if phones sold in the country were not made within its borders.

Shares of Apple dropped 2.5% in premarket trading on Trump's warning, dragging down U.S. stock index futures lower.

"I have 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," Trump said in a post on Truth Social.

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

It is not clear if Trump can levy a tariff on an individual company. Apple did not immediately respond to a Reuters request for comment.

Apple is positioning India as an alternative manufacturing base amid Trump's tariffs on China that have raised supply-chain concerns and fears of higher iPhone prices, Reuters reported last month.

The iPhone maker said most of its smartphones sold in the United States would originate from India in the June quarter.

(Reporting by Akash Sriram in Bengaluru; Editing by Shilpi Majumdar and Anil D'Silva)