New York, May 24 -- U.S. stocks closed lower, ending the week with losses as investors reacted to U.S. President Donald Trump's new tariff threats.

Trump commented on Friday that Apple must pay a 25 percent tariff on iPhones sold but not made in the United States.

In the afternoon, Trump signaled that potential tariffs on mobile phones would not just target Apple but extend to other manufacturers like Samsung, stating, "It would be more, it would be also Samsung and anybody that makes that product, otherwise it wouldn't be fair." He added that companies that build manufacturing plants in the United States would be exempt from tariffs.

Trump also threatened to raise tariffs on European Union imports to a flat 50 percent starting June 1, a...