North Korea launched several ballistic missiles toward the Sea of Japan on Monday, South Korea's military said.

South Korea's Joint Chiefs of Staff said in a statement that its forces detected the launches at around 09:20 (00:20 GMT) from the Pyongyang area, heading toward the "East Sea", the Korean name for the Sea of Japan. The military said it had "strengthened surveillance and vigilance in preparation for possible additional launches."

Earlier the same day, the Joint Chiefs had issued a brief statement saying the North had fired an unidentified projectile in the same direction.

The launches come days after North Korea tested an intermediate-range hypersonic missile, according to Agence France-Presse. Pyongyang said the October 3 launch involved the use of artificial intelligence, adding that the missile was "capable of changing its flight path at low altitude."

Days later, South Korea carried out its first test launch of a domestically developed hypersonic missile. The presidential Blue House said President Lee Jae-myung observed the first test of a hypersonic glide vehicle currently being researched and developed with home-grown technology.

The statement described the weapons system as "a core strategic capability that can change the course of a battle," saying the unpredictable flight paths and extreme speed of its warheads allow it to strike key strategic targets.

Hypersonic glide vehicles are carried into the upper atmosphere by booster rockets before gliding toward their targets at five times the speed of sound or faster.