North Korea fired multiple missiles off its east coast, which flew about 1,000 km (620 miles), South Korea's military said on Monday.
The missiles were launched from the area of Tongchang-ri, where a missile base is located, the military said, but it did not provide the number of the North Korean missiles.
"South Korea and the United States are conducting a close-up analysis, regarding further information," South Korea's Office of Joint Chiefs of Staff said in a statement.
The missiles, which landed in the sea off North Korea's east coast, are possible retaliation by the reclusive state to joint U.S.-South Korean drills that began last week.
Tongchang-ri is near the North's border with China, where the isolated state fired a long-range rocket last year that put an object into orbit. The launch was condemned by the United Nations for violating resolutions that ban the use of missile technology.
North Korea has threatened to take "strong retaliatory measures" after South Korea and the United States began annual joint military drills on Wednesday that test their defensive readiness against possible aggression from the North.
North Korea criticizes the annual drills, calling them preparation for war against it.Try Newsweek: Subscription offers