U.S. President Donald Trump has approved South Korea’s plan to build a nuclear-powered submarine, a significant shift from the diesel-powered vessels currently in use.

The announcement came during his meeting with South Korean President Lee Jae Myung in Gyeongju, where the leaders also discussed broad trade and investment deals.

Trump said the submarine would be built in Philadelphia, but details about nuclear propulsion technology and fuel remain unclear, raising proliferation and safety concerns, The Guardian has reported.

Experts noted the move would require strict safeguards under the Non-Proliferation Treaty and stressed that South Korea’s submarines would not be nuclear-armed.