The move will only add to tensions in the region already heightened by the North's recent barrage of weapons tests.
Additionally, Seoul's military said it had scrambled fighter jets when around 10 North Korean military aircraft flew close to the border between the two countries. By Friday evening local time, Seoul also reported the North was firing dozens of artillery rounds into waters near the eastern maritime border and nearly 200 rounds near the western sea border.
The development comes less than 24 hours after North Korean leader Kim Jong Un supervised long-range cruise missile tests.
Kim described the tests as a demonstration of Pyongyang's readiness for "actual war."
Meanwhile, South Korea's National Security Council condemned the North for escalating tension, calling its moves a violation of a 2018 bilateral military pact that bans "hostile acts" in the border area.
It also added that North Korea's provocations must come at a price. Seoul imposed its first unilateral sanctions against Pyongyang in nearly five years, blacklisting 15 North Korean individuals and 16 institutions involved in missile development.
What North Korea said about the missile launch
Shortly after the missile launch in the early hours of Friday morning local time, North Korea said it came in response to its southern neighbor "inciting military tension," state media reported.
A North Korean army spokesman said the South Korean army on Thursday had conducted "artillery fire for about 10 hours near the forward defence area of the KPA Fifth Corps," according to a statement carried by the Korean Central News Agency.
The Korean People's Army (KPA) "took strong military countermeasures" as a response to the "provocative action," the statement continued.
The KPA "sends a stern warning to the South Korean military inciting military tension in the frontline area with reckless action."
jsi/rt (AP, AFP, dpa, Reuters)