"North Korea fires an unidentified ballistic missile towards (the) East Sea," South Korea's Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.

Trump had announced that South Korea would build the submarine in the United States, where the nuclear technology is among the most sensitive and tightly guarded military secrets.

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

Analysts say developing a nuclear-powered submarine would mark a significant leap in South Korea's naval and defence industrial-base, joining a select group of countries with such vessels.

Only the United States, Australia, China, Russia, India, France and Britain have moved toward nuclear-powered submarines, according to media and analysis reports.

South Korea's presidential office has said Seoul needed Washington's approval as it requires the raw material needed to build a nuclear-powered submarine, which is restricted for military use.

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.