U.S. President Donald Trump has approved South Korea’s construction of a nuclear-powered submarine.

In a post on the social media platform Truth Social on Thursday, Trump wrote that the South Korea–U.S. military alliance is stronger than ever before, adding that he has given South Korea approval to build nuclear-powered submarines instead of the old-fashioned, and far less nimble, diesel-powered submarines it currently operates.

Trump added that the submarine will be built in Philadelphia and that U.S. shipbuilding will soon make a big comeback.

The announcement comes a day after President Lee Jae Myung requested that Washington relax its restrictions on Seoul’s procurement of nuclear fuel for nuclear-powered submarines during his summit with Trump in Gyeongju.

Trump also said that South Korea has agreed to pay the United States 350 billion U.S. dollars in exchange for reduced tariffs.

He added that Seoul has agreed to purchase vast quantities of U.S. oil and gas, and that wealthy South Korean companies' and business owners' investment in the U.S. will exceed 600 billion dollars.