Seoul, Mar 15 (IANS): North Korea has launched two ground-to-ground ballistic missiles in a demonstration drill designed to train sub-military units, vowing to "annihilate the enemy", Pyongyang's state media said on Wednesday.

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

South Korea's military said on Tuesday that the North fired two short-range ballistic missiles from the Jangyon area toward the East Sea, a day after Seoul and Washington kicked off a regular joint military exercise.

The North said the missiles hit a pre-set target on an islet off its east coast after travelling some 611 km.

Photos carried by the North's state media showed the North firing what appears to be KN-23 missiles, its version of the Russian Iskander, from a transporter erector launcher (TEL).

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

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

Pyongyang has decried the Seoul-Washington exercises as rehearsal for an invasion against it and threatened to take "overwhelming" action against military activities by the allies.