Busan, South Korea - The US will allow South Korea to build nuclear-powered submarines, President Donald Trump said on Wednesday, calling the allies' defence partnership "stronger than ever."

The submarines will be built in Philadelphia, Trump wrote in a post on his Truth Social platform.

"I have given them approval to build a Nuclear Powered Submarine, rather than the old fashioned, and far less nimble, diesel powered Submarines that they have now," he added in a different post, which has since been removed.

South Korean President Lee Jae Myung had asked Trump during their meeting on Wednesday for access to fuel for nuclear submarines. According to Seoul's national security adviser Wi Sung Lac, Trump agreed in principle but called for further discussions.

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Exporting nuclear fuel for submarine use is politically sensitive, as it often involves highly enriched uranium – the same material used in nuclear weapons.

Nuclear-powered submarines can remain submerged for several months, giving them a strategic advantage over conventional diesel-powered vessels.

The move underscores the deepening security ties between Washington and Seoul as China's influence in the Indo-Pacific grows. During his Asia tour, Trump also pledged to expand defense and economic cooperation with Japan.

Trump further said that South Korea had agreed to provide $350 billion to the US in exchange for lower tariffs on South Korean imports. According to Seoul, $200 billion would be paid in cash and the rest invested in joint shipbuilding projects.

He added that South Korean companies and investors would commit an additional $600 billion in US investments.