North Korea fired a submarine-launched ballistic missile Saturday, Seoul said, its second missile launch in three days, after the US warned Pyongyang could be preparing for a nuclear test.

Pyongyang has dramatically ramped up its sanctions-busting missile launches this year, conducting 15 weapons tests since January including firing an intercontinental ballistic missile at full range for the first time since 2017.

The latest launch comes just days before South Korea swears in a new, hawkish President Yoon Suk-yeol, who has vowed to get tough on Pyongyang and bolster the US security alliance.

Satellite imagery indicates North Korea may also be preparing to resume nuclear testing, with the US State Department on Friday warning a test could come “as early as this month”.

“Our military detected around 14:07 (0507 GMT) a short-range ballistic missile presumed to be an SLBM fired from waters off Sinpo, South Hamgyong,” Seoul’s Joint Chiefs of Staff (JCS) said in a statement.

Sinpo is a major naval shipyard in North Korea and satellite photos have in the past shown submarines at the facility.

The missile flew 600 kilometres (372 miles) at a maximum altitude of 60 kilometres, the JCS added, a distance that indicates it was a short-range ballistic missile.

It landed outside Japan’s exclusive economic zone, Tokyo’s Defence Minister Nobuo Kishi said.

He added that the “extremely high frequency” of tests by North Korea this year was “absolutely unacceptable”.

Pyongyang’s “remarkable development of nuclear and missile-related technology” is a regional and global security risk, he said, adding that Japan also believed “North Korea will be ready to carry out a nuclear test as early as this month”.