Pyongyang says it launched five "missiles" into Sea of Japan amid widespread concerns about its nuclear programme.
South Korea disputed Pyongyang's description of the projectiles as "missiles" on Monday, saying instead the objects were smaller "short-range projectiles" - most likely conventional shells.
South Korean officials said the five projectiles flew about 200 kilometers after being launched from an area about 20km south of Hamhung on Monday afternoon local time.
Tensions have been soaring on the divided Korean peninsula since the North carried out its fourth nuclear test on January 6, followed a month later by a long-range rocket launch that was widely seen as a disguised ballistic missile test.
The UN Security Council responded earlier this month by imposing its toughest sanctions on North Korea to date.
In recent weeks Pyongyang has maintained a daily barrage of nuclear strike threats against both Seoul and Washington, ostensibly over continuing large-scale South Korea-US military drills that the North sees as provocative rehearsals for invasion, foreign media reports.