North Korea fired "several" ballistic missiles on Monday toward the sea off its east coast, South Korea's military said.
A Japanese government alert and its coast guard also said North Korea had fired what appeared to be a ballistic missile.
The projectile appeared to have landed outside Japan's exclusive economic zone area, the NHK broadcaster said.
Japan's NTV broadcaster said the projectile was a short-range ballistic missile, citing a Japanese government official.
South Korea's Joint Chiefs of Staff said the North launched what it suspected to be several short-range ballistic missiles from near its capital, Pyongyang, without providing further details.
The reports of the launch came as South Korea said its top military officer, Admiral Kim Myung-soo, had hosted the commander of U.S. Space Command, General Stephen Whiting, on Monday to discuss the North's reconnaissance satellite development and growing military cooperation between Pyongyang and Moscow.
After a summit between the two countries' leaders in September, North Korea has been suspected of supplying arms and munitions to Russia for its invasion of Ukraine, although both deny that claim.
The North is believed to be preparing to launch another spy satellite, after successfully putting a reconnaissance satellite in orbit in November.
North Korea said last week that it had fired a strategic cruise missile to test a large warhead, and a new anti-aircraft missile.
Earlier in April, the North fired a new hypersonic missile as part of its development of solid-fueled missiles for all ranges of its arsenal.
The North has defied a ban by the United Nations Security Council on developing ballistic missiles, rejecting Council resolutions as infringing on its sovereign right to defend itself.
