North Korea fired two short-range ballistic missiles off its east coast on Wednesday, the South's military said, just a day before US Vice President Kamala Harris is set to arrive in Seoul.
After a stop in Japan, Harris is set to arrive in the South Korean capital and visit the heavily fortified Demilitarized Zone (DMZ) between the neighbors on Thursday.
Japan's coast guard also reported a suspected ballistic missile test.
The launch came two days after South Korea and US forces launched a military drill in waters off the South's east coast involving an aircraft carrier. On Sunday, North Korea had fired another ballistic missile towards the sea off its east coast.
In a speech hours earlier aboard the destroyer USS Howard destroyer in the Japanese city of Yokosuka, Harris said Sunday's launch was part of an "illicit weapons program which threatens regional stability and violates multiple UN Security Council resolutions".
Since 2006, North Korea has been subject to UN sanctions, 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 the UN resolutions as an infringement of its sovereign right to self-defense and space exploration, and has criticized military exercises by the United States and South Korea as proof of their hostile intentions.