North Korea launched two ballistic missiles eastward early on Wednesday, and both of them appeared to have fallen outside Japan's exclusive economic zone, the Japanese Defence Ministry said.
The U.S. 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 programme, the U.S. Indo-Pacific Command said in a statement.
The first missile reached an altitude of 50 km (31 miles) and covered a range of 550 km, while the second one rose as high as 50 km and flew 600 km, Japanese Defence Minister Yasukazu Hamada told reporters.
Japan lodged a protest against the missile launches through diplomatic channels, he said.
The firing comes nearly a 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.
Wednesday's launch came a day after a U.S. nuclear-armed ballistic missile submarine visited South Korea for the first time since the 1980s.
Also on Tuesday, a U.S. 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 fresh crisis between the two foes.
