North Korea has conducted two ballistic missile launches in recent days. (Source: KCNA)

Yonhap news agency quoted the South Korean Joint Chiefs of Staff (JCS) as saying that they detected these launches at 6:50 a.m. on September 18 local time (4:50 a.m. on the same day Vietnam time) in the Kaechon area in South Phyongan province, north of the North Korean capital Pyongyang.

However, the report did not provide further details, including the number of missiles launched. The JCS said the South Korean military will share information on North Korea's ballistic missiles with the United States and Japan and maintain a readiness posture.

On Japan's side, the country announced that North Korea launched two unidentified ballistic missiles, both of which fell into the sea.

NHK news agency quoted government sources as saying that both missiles fell outside Japan's Exclusive Economic Zone (EEZ), but did not provide details on the missiles' flight direction and trajectory.

The launch took place in the context that last week, North Korean President Kim Jong-un inspected a number of nuclear facilities in the country, in which he requested to promote and strengthen nuclear capabilities to deal with external threats.

Just one day before this inspection, Pyongyang also test-fired a new 600mm multiple rocket system.