North Korea fired two short-range ballistic missiles from its capital Pyongyang toward the east coast on Wednesday, South Korea's military said.
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 programs.
North Korea rejects UN resolutions as an infringement of its sovereign right to self defense and space exploration, and has criticized military exercises by United States and South Korea as proof of their hostile intentions.