North Korea fired a ballistic missile off its east coast on Wednesday, South Korea's military said, as South Korea and the US staged joint naval exercises involving an aircraft carrier.
Japan's coast guard also reported a suspected ballistic missile test.
The launch came two days after South Korea and US forces launched their military exercise in the waters off South Korea's east coast involving an aircraft carrier.
US Vice President Kamala Harris is set to arrive in the South Korean capital, Seoul, on Thursday after a visit to Japan.
North Korea also fired a ballistic missile towards the sea off its east coast on Sunday.
North Korea has been subjected to UN sanctions since 2006, which the Security Council has steadily - and unanimously - stepped up over the years to cut off funding for its nuclear weapons and ballistic missile programmes.
North Korea rejects UN resolutions as an infringement of its sovereign right to self defence and space exploration, and has criticised military exercises by United States and South Korea as proof of their hostile intentions.