US President Donald Trump last week said he had given ally Seoul a green light, after South Korea had announced that the two countries reached a broad deal covering investment and shipbuilding.

Trump, who was in South Korea for a regional summit, said on Truth Social that Seoul would manufacture its nuclear-powered submarine in "the Philadelphia Shipyards, right here in the good ol' U.S.A."

US nuclear submarine technology is considered among the most sensitive and tightly guarded military secrets.

Unlike diesel-powered submarines which must surface regularly to recharge their batteries, nuclear-powered ones can remain submerged for far longer periods of time.

Seoul has not commented on Trump's remarks suggesting the submarine would be built on US soil.

Senior defence ministry official Won Chong-dae, however, said on Tuesday that it was "feasible to construct a nuclear-powered submarine with our own technology".

"If we secure the submarine fuel through consultations with the United States and enter the construction phase in the late 2020s, we expect to launch the lead vessel by the mid to late 2030s," Won told a cabinet meeting.

"South Korea already possesses world-class design and construction capabilities for conventional submarines," he said.

His remarks came after a South Korean presidential aide said Seoul had sought Washington's "authorisation for the raw materials" and received approval.

- Denuclearisation 'pipedream' -

The Philadelphia shipyard mentioned by Trump has been run by South Korea's Hanwha Ocean since last year, but media reports say it lacks the facilities and equipment needed to build nuclear-powered submarines.

In August, Hanwha Ocean announced a $5 billion investment in the shipyard, describing it as part of Seoul's commitment to supporting shipbuilding growth in the United States, which Trump has pushed for.

Pentagon chief Pete Hegseth, who visited the border between the two Koreas earlier this week, said on Tuesday that Seoul has "an incredible shipbuilding industry which we look forward to partnering with a lot more."

Since North Korean leader Kim Jong Un's 2019 summit with Trump collapsed over the scope of denuclearisation and sanctions relief, Pyongyang has repeatedly declared itself an "irreversible" nuclear state.

It has since forged closer ties with Russia, sending troops to support Moscow's war in Ukraine, and did not respond to Trump's offer to meet with Kim last week.

Pyongyang also dismissed Seoul's hopes for denuclearisation as a "pipedream" which "can never be realised".

Seoul's Defence Minister Ahn Gyu-back said Tuesday that denuclearisation of the Korean Peninsula "remains an unwavering commitment", and ruled out South Korea ever possessing nuclear arms.