North Korea has fired what has been described as an unidentified projectile into the sea, said South Korea’s Joint Chiefs of Staff (JCS).
The Japanese coast guard, which first reported the launch, said it could potentially be a ballistic missile, but no confirmation has yet been given.
The UN prohibits North Korea from ballistic and nuclear weapons tests.
If confirmed, this would be the first such launch carried by Pyongyang this year.
“South Korean and US intelligence are closely analysing for further detail,” the JCS said in a statement.
Japan’s defence minister Nobuo Kishi said the suspected ballistic missile had flown about 500 km (310 miles), according to a Reuters report, but according to one expert, there is still no way to confirm this.
“There’s no way to assess whether this might have been a longer-range missile flown on a shortened trajectory,” Ankit Panda of the Nuclear Policy Programme at the Carnegie Endowment for International Peace told BBC News.
In 2017, North Korea tested the Hwasong-15, a missile that peaked at an estimated altitude of 4,500km, putting US military bases on the Pacific island of Guam well within striking distance.
The launch comes days after Mr Kim said that Pyongyang would continue to strengthen its defence capabilities due to an increasingly unstable military environment on the Korean peninsula – a stance Mr Panda warned could see 2022 “littered with similar North Korean missiles.”
Mr Kim made the remarks during a key end-of-year meeting of North Korea’s ruling party.
Japanese Prime Minister Fumio Kishida called the latest launch “very regrettable,” pointing to North Korea’s repeated testing of missiles since 2021.
In 2021, North Korea continued the advancement of its weapons programme, conducting what state media reported as the testing of a new hypersonic missile, as well as a train-based ballistic missile and a new long-range cruise missile.
Ballistic missiles are considered more threatening than cruise missiles because they can carry more powerful payloads, have a longer range and can fly faster.
What’s the situation in North Korea?
The tests come as Pyongyang struggles with food shortages due to a coronavirus blockade that has affected its economy.
At the end-of-year meeting, Mr Kim said the country was facing a “great life-and-death struggle”, adding that increasing development and improving people’s living standards were among this year’s goals.
United Nations officials had earlier warned that vulnerable children and elderly people in North Korea were at risk of starvation.
However, Mr Panda says this was unlikely to deter North Korea from pursuing its weapons program.
“[Mr] Kim has maintained his emphasis on self-reliance in national defence in recent years even as he has been open about economic difficulties in the country,” Mr Panda said.
“For [Mr] Kim and the Workers’ Party, sustaining these weapons programs is a top national priority for both internal and external reasons.”
The US has been calling for North Korea to give up its nuclear weapons, and Pyongyang’s relationship with President Joe Biden’s administration has so far been fraught with tension.
North Korea has also repeatedly accused South Korea of double standards over military activities.
South Korea recently tested its first submarine-launched ballistic missile, which it said was needed as deterrence against North Korea’s “provocations”.