North Korea has launched two ballistic missiles, Japan’s and South Korea’s militaries say, hours after a US ballistic missile submarine arrived in a South Korean port for the first time in four decades.

Both of the missiles appeared to have fallen outside Japan’s exclusive economic zone, the Japanese Defence Ministry said on Tuesday.

South Korea’s Joint Chiefs of Staff (JCS) called on the North 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 United Nations Security Council resolutions,” the JCS said in a statement.

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

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

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

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

The firing comes nearly one week after North Korea tested its latest Hwasong-18 intercontinental ballistic missile, a launch Pyongyang said was a warning to the United States and other adversaries.