North Korea fired at least one ballistic missile into the sea on Wednesday, as South Korea said it had identified debrisfrom an earlier launchas 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 50km, and covered a range of 250km, Japan's Defence Minister Yasukazu Hamada told reporters.
He said the government lodged a strong protest with North Korea via diplomatic channels through Beijing, and that Tokyo had strongly condemned the launch.
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 strongly condemned the missile launch at the time, calling it a breach of 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."
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), protesting against joint air drills by South Korea and the US.
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 exercises as an "dangerous, aggressive war drill."
South Korean and US 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."