South Korea has criticised North Korea for test-firing a submarine-launched ballistic missile, Efe news agency reported on Monday.
It has also urged Kim Jong-un's regime to halt development of such weapons.
The North Korean missile test, announced by Pyongyang on Saturday and carried out at an undisclosed location and date, was "very serious and worrying", said a South Korean defence ministry spokesperson in a press conference on Monday.
"We urge the North to immediately stop development of the SLBM (submarine-launched ballistic missile) that threatens the security of the Korean Peninsula and northeast Asia," said the spokesperson.
The launch suggests the North Korean regime has developed the technology needed to fire ballistic missiles from submarines.
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This test-firing, personally directed by North Korean leader Kim Jong-un according to state news agency KCNA, has raised tensions on the peninsula, with South Korean armed forces boosting preparations against an attack from its neighbour.
Last week, the Communist country threatened to open fire without warning on South Korean naval ships that cross a disputed Yellow Sea border for "spy purposes".
In recent days, South Korea has announced its intention to commission nine 3,000-tonne submarines capable of launching ballistic missiles, the first in 2020.
Pyongyang boasts of a fleet of 70 submarines, including 20 of 1,800 tonnes, against South Korea's four 1,800-tonne and nine 1,200-tonne vessels.
North and South Korea are technically still at war as the armistice that ended the Korean War in 1953 was never followed by a definitive peace treaty.
