Japan's military said Wednesday it detected North Korea test-firing two ballistic missiles, adding to its military demonstrations as tensions with Washington and neighbours escalate.

The launches come days after North Korea offered a rare view into a secretive facility built to enrich uranium for nuclear bombs in a significant show of defiance against the United States and as leader Kim Jong Un called for a rapid expansion of his nuclear weapons program.

Japan's Defence Ministry didn't immediately provide more details about the weapons involved in the North's latest test, including what types of missiles they were and how far they flew.

Japan's coast guard said the missiles were believed to have already fallen into waters between the Korean Peninsula and Japan and urged vessels to watch out for falling objects. Japan's NHK television said the missiles were believed to have landed outside of Japan's exclusive economic zone.

The launches followed a previous round of ballistic tests last week as Kim vowed to have his nuclear force fully ready for battle with its rivals.

Since 2022, North Korea has ramped up its weapons testing activities to expand and modernise its arsenal of nuclear missiles targeting the US and South Korea.

Analysts say North Korea could conduct a nuclear test explosion or long-range missile test ahead of the US presidential election in November with the intent of influencing the outcome and increasing its leverage in future dealings with the new US administration.