Both of the missiles launched early on Wednesday morning appeared to have fallen outside Japan’s exclusive economic zone, the Japanese defence ministry said.

South Korea’s Joint Chiefs of Staff (JCS) called on North Korea to cease such launches.

“We strongly condemn North Korea’s successive ballistic missile launches as grave provocative acts that undermine the peace and stability of the Korean Peninsula as well as the international community, and are a clear violation of UN Security Council resolutions,” the JCS said in a statement.

The first missile reached an altitude of 50km (31 miles) and covered a range of 550 km (341 miles), while the second one rose as high as 50km and flew 600km (372 miles), Japanese Defence Minister Yasukazu Hamada told reporters.

Japan has lodged a protest against the missile launches through diplomatic channels, he said.

Video Duration 01 minutes 54 seconds01:54North Korea conducts second test of solid-fuel missiles

The launches come nearly a week after North Korea test-fired its latest Hwasong-18 solid-fuel intercontinental ballistic missile, which Pyongyang said was a warning to the US and other adversaries.

South Korea’s Yonhap News Agency reported that the missile launch on Wednesday followed Seoul and Washington’s first meeting of the Nuclear Consultative Group (NCG), which is aimed at strengthening the US’s “extended deterrence commitment to using the full range of its military capabilities, including nuclear weapons, to defend its ally” South Korea.

That meeting also coincided with the arrival of USS Kentucky at a naval base in Busan, “the first port visit by an American nuclear-capable strategic submarine (SSBN) since USS Robert E. Lee in March 1981”, Yonhap reported.

The US military said that it was aware of the missile launches on Wednesday morning and was consulting closely with its allies and partners.

The launches did not appear to pose an immediate threat to the US or its allies but the events highlight the destabilising impact of North Korea’s illicit weapons programme, the US Indo-Pacific Command said in a statement.

On Tuesday, a US soldier facing disciplinary action fled across the inter-Korean border into North Korea. The soldier is believed to be in North Korean custody, Washington said, creating a new crisis between the two foes.

Leif-Eric Easley, professor of international studies at Ewha University in Seoul, said the latest launch had more to do with the arrival of the US submarine and the meeting on Washington’s extended deterrence to South Korea.

“North Korea’s latest firing of ballistic missiles is probably unrelated to an American soldier crossing the inter-Korean border, but such an incident doesn’t help matters either,” Easley said in a statement.

“As Pyongyang looks to assert its nuclear threats and capabilities over South Korea, it undoubtedly opposes Seoul and Washington’s Nuclear Consultative Group and the visit of a US nuclear ballistic missile submarine,” he said.