Trump, who has been meeting with South Korean President Lee Jae Myung and other regional leaders during his visit, also said Seoul had agreed to buy vast quantities of US oil and gas.

Trump and Lee finalised details of a fraught trade deal at a summit in South Korea on Wednesday.

Lee had also been seeking US permission for South Korea to reprocess nuclear fuel to power submarines that could track North Korean and Chinese vessels for longer periods.

Seoul is barred from reprocessing without US consent, under a pact between the countries.

“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,” Trump wrote on his Truth Social platform on Thursday.