North Korea has launched two ground-to-ground ballistic missiles in a demonstration firing drill for sub-military units, vowing to "annihilate the enemy," according to state media Wednesday.

A missile unit of the North's military launched the missiles "in a medium-range system" Tuesday in Jangyon, South Hwanghae Province, according to the official Korean Central News Agency.

South Korea's military said Tuesday the North fired two short-range ballistic missiles toward the East Sea, and they flew some 620 kilometers.

The North's provocation came a day after the South and the United States kicked off a regular joint military exercise, called the Freedom Shield.

Photos carried by the North's state media showed the North firing what appears to be KN-23 missiles from a transporter erector launcher.

The North said it will "surely annihilate the enemy" if its military fights against its enemy and vowed to "fully carry out its duty of fire assault any time" by intensifying fire assault training, the KCNA said.

The latest launch came after the North fired what it claimed to be two "strategic cruise missiles" from a submarine Sunday and conducted a "fire assault drill" three days earlier.

Pyongyang has decried the exercises as a rehearsal for a war of aggression against it and threatened to take "overwhelming" action against military activities by the allies. (Yonhap)