The missiles were launched from Wonsan, North Korea's eastern coastal city, on Thursday morning and flew up to 800km before splashing down in the sea, the military said in a statement.
South Korea was closely communicating with the US and Japan to share information about the launch, it said.Â
The foreign ministry said the three countries' nuclear envoys consulted by telephone and condemned it as a violation of UN sanctions.
South Korean Joint chiefs of Staff spokesman Lee Sung-jun declined to comment on the exact number of missiles detected or their characteristics, but told reporters the launch might have been to test the performance of missiles intended for export.
A North Korea analyst at the Korea Institute for National Unification, Hong Min, said they were likely two types of short-range ballistic missiles that had been supplied to Russia which used them to strike Ukraine.
"There is considerable amount of field data of these two missiles collected, and it's possible additional testing was needed to improve issues reported from the battlefield such as durability and precision," Hong said.
The Japanese government also said it detected a launch of a ballistic missile by North Korea, which might have flown on a irregular trajectory.
The nuclear-armed North's ballistic missile program is banned by United Nations Security Council resolutions, but in recent years Pyongyang has forged ahead with developing missiles of all ranges.
In March, North Korea fired multiple ballistic missiles, while blaming the South Korean and US militaries for conducting drills it calls dangerous and provocative.
North Korea has exported short-range ballistic missiles, among other weapons, to Russia for use in the war in Ukraine, according to US and allied intelligence agencies as well as independent researchers.
Pyongyang and Moscow have denied the weapons trade, although North Korean troops have been deployed to fight on the front lines in Russia's Kursk region.
