North Korea fired at least one ballistic missile into the sea on Wednesday, as South Korea said it had identified debris from an earlier launch as part of a Soviet-era SA-5 surface-to-air missile.
Japan's Coast Guard said the ballistic missile appeared to have fallen into the sea minutes after the launch was reported.
The missile flew to an altitude of up to 50 km (31.07 miles), and covered a range of 250 km, Japan's Defence Minister Yasukazu Hamada told reporters.
He said the government lodged a strong protest with North Korea via diplomatic channels through Beijing.
Seoul's Joint Chiefs of Staff (JCS) also said it had detected the launch of an unspecified ballistic missile from North Korea.
The launch came after South Korea concluded an analysis of what it had initially said was part of a North Korean short-range ballistic missile (SRBM) that landed near South Korean waters last week.
The analysis, however, showed the piece, about 3 metres (3.3 yards) long and 2 metres wide, was part of an SA-5 anti-aircraft missile, the defence ministry said, citing its appearance and features.
The ministry said at the time the launch breached a 2018 inter-Korean military pact banning any activities stoking border tensions.
"This SA-5 missile launch was a clearly deliberate, intentional provocation," it said in a statement. "The SA-5 also has characteristics of a surface-to-surface missile, and Russia has used similar missiles in Ukraine for surface-to-surface attacks."
The U.S. Indo-Pacific Command said in a statement it was aware of the launch and assessed it did not pose an immediate threat to U.S. personnel or territory, or to its allies. It also denounced Pyongyang's missile programs as having a destabilizing effect.
A South Korean Navy ship used an underwater probe to recover the missile, which came as the North test-fired multiple missiles last week, including a possible failed intercontinental ballistic missile (ICBM)
It was the first time a North Korean ballistic missile had landed near South Korean waters.
North Korea's military said the launches were simulated strikes on South Korea and the United States, criticising their joint air exercises as an "dangerous, aggressive war drill."
South Korean and U.S. officials have also said that Pyongyang has made technical preparations to test a nuclear device, the first time it will have done so since 2017.
The SA-5 is an air defence missile originally designed by the Soviet Union, where it was designated the S-200, to shoot down strategic bombers and other high-altitude targets.
The missile was exported around the world, and is still in service in at least a dozen countries, according to the Center for Strategic and International Studies' Missile Defense Project.
North Korea took delivery of SA-5 systems in the mid-1980s, according to "The Armed Forces of North Korea: On the Path of Songun", a 2020 survey by Dutch researchers.
"Two sites equipped with these very long-ranged systems cover the entirety of North Korean airspace as well as a sizeable chunk of that of the South," the researchers wrote.
"However, having been designed to counter strategic aircraft, their use against modern fast jets such as the F-15 and F-16 is questionable to say the least."
(Reporting by Hyonhee Shinn and Josh Smith; Additional reporting by Kantaro Komiya and Daniel Leussink in Tokyo; Editing by Lincoln Feast, Gerry Doyle and Tomasz Janowski)
