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

Tokyo also confirmed the launch, with the defence ministry saying that Pyongyang had launched a "possible ballistic missile," without giving further details.

Military tensions have risen on the Korean peninsula after a year in which North Korea declared itself an "irreversible" nuclear state, and carried out sanctions-busting weapons tests nearly every month.

In response, Seoul has ramped up joint military drills with key security ally Washington, in a bid to convince the increasingly nervous South Korean public of America's commitment to deter Pyongyang.

The Saturday launch -- Pyongyang's first since January 1 -- came days before Seoul and Washington are due to kick off a new tabletop exercise in Washington, in which the two allies will discuss how they would respond to the use of nuclear weapons by Pyongyang.

The exercise next week will focus on "joint planning, joint management and joint response with Washington's nuclear assets" in case of a nuclear attack by Pyongyang, a South Korean defence ministry official told AFP on Friday.

Pyongyang on Friday threatened an "unprecedentedly" strong response to upcoming US-South Korea drills, describing them as preparations for war.

If Washington and Seoul go ahead with the drills, "they will face unprecedentedly persistent and strong counteractions", a spokesperson for the North Korean foreign ministry said Friday.

South Korea's hawkish President Yoon Suk Yeol, who took office in May 2022, has vowed to get tough on the North, and had moved to quickly ramp up joint drills, which had been scaled back during the Covid pandemic.

They were also paused for a bout of ill-fated diplomacy with Pyongyang under his predecessor.

- No talks, more missiles -

South Korea also called the nuclear-armed North its "enemy" in a defence document earlier this week, the first time in six years it has used the term, signalling a further hardening of Seoul's position toward Pyongyang.

North Korea's missile tests last year also included one that landed near South Korea's territorial waters for the first time since the end of the Korean War in 1953.

In December, it sent five drones across the border into Seoul's airspace, including skies near its presidential office.

Pyongyang has repeatedly said it is not interested in further talks, and North Korean leader Kim Jong Un recently called for an "exponential" increase in his country's nuclear arsenal.

At a military parade in Pyongyang last week, North Korea showed off a record number of nuclear and intercontinental ballistic missiles, including what analysts said was possibly a new solid-fuelled ICBM.

The weapons on show included at least 10 of the North's largest Hwasong-17 ICBMs, as well as vehicles apparently designed to carry a solid-fuelled ICBM.

North Korea has long sought to develop a solid-fuel ICBM because such missiles are easier to store and transport, are more stable and quicker to prepare for launch, and thus harder for the United States to detect and destroy pre-emptively.