North Korea on Monday fired multiple ballistic missiles off its east coast, Seoul's military said, after weeks of mounting friction over a landmine explosion along the countries' heavily fortified border.
"Our military detected around 09:20 (00:20 GMT) several ballistic missiles launched from the Pyongyang area towards the East Sea," the Joint Chiefs of Staff said in a statement, referring to the Sea of Japan.
"Our military has stepped up surveillance and vigilance against possible additional launches," it added.
Japan's defence ministry separately confirmed the launch of at least one suspected ballistic missile.
Tensions between the two Koreas have soared since three South Korean soldiers were injured last month when two landmines detonated in the Seoul-controlled area of the Demilitarised Zone (DMZ) that divides the two countries.
A joint Seoul-UN investigation concluded that North Korea had planted the landmines over a year ago, something Pyongyang has angrily denied.
Read moreNorth Korea launches ballistic missile as tensions with Seoul grow over border mine blasts
Pyongyang has since launched a ballistic missile it says incorporated artificial intelligence, while Seoul last week announced the successful test of its first homegrown hypersonic weapon.
Kim Yo Jong, powerful sister of North Korean leader Kim Jong Un, said the North's October 3 launch featured a missile "capable of changing its flight orbit at a low altitude and AI was introduced into it".
Seoul said days later that it had tested a domestically produced hypersonic glide vehicle (HGV), a weapon carried into the upper atmosphere by rocket boosters or ballistic missiles before gliding towards its targets.
South Korea's presidential office said the HGV offered "a new deterrence capability capable of striking key targets within the Korean Peninsula's operational environment".
Since the September 21 landmine incident, Seoul has demanded an apology, something Kim Yo Jong has blasted as "despicable, while rejecting a planned transfer of medical equipment from Seoul.
"If they (South Korea) truly wish to restore relations between the DPRK and South Korea, they should be mindful of the other side's feelings in every word and deed, and first demonstrate the utmost respect, consideration and sincerity," she said Thursday, using her country's official acronym.
The DMZ is one of the world's most heavily fortified frontiers, and landmine incidents have previously heightened tensions between the two Koreas.
Seoul and Pyongyang remain technically at war since the Korean conflict ended in 1953 with a truce, not a peace treaty.
(FRANCE 24 with AFP)