Seoul, Mar 2 (IANS): North Korea on Thursday warned that it will respond with "merciless military counter-action" to the annual joint military exercises that South Korea and the US are conducting on the Korean peninsula.

The Korean People's Army (KPA) has said it will "counter (the drills) with the toughest counteractions" targeting South Korea, the USs and its "vassal states" participating in the exercises known as Key Resolve and Foal Eagle, a KPA spokesman said in a statement released by state news agency KCNA.

"Should the US imperialists and the South Korean puppet forces fire even a single shell into the waters where the sovereignty of our Republic is exercised, the KPA will immediately launch its merciless military counter-actions," according to the statement.

Seoul and Washington began their annual joint military drill on Wednesday, codenamed "Foal Eagle", which includes aerial, ground and naval maneuvers. The drills are likely to continue through the end of April, Efe news reported.

Pyongyang accused South Korea and the US of rehearsing a "preemptive attack" on the North by conducting the defensive military simulation, and also denounced the weapons installations in the region, including Terminal High Altitude Area Defense (THAAD), a missile defence system due to be deployed in South Korea this year.

The KPA statement, which accused Washington of attempting to wage a nuclear war, added that it will "foil the nuclear war racket of the aggressors with its treasured nuclear sword of justice".

The military drills are being held in the wake of the February 13 assassination in Malaysia of Kim Jong-nam, half-brother of the North Korean leader Kim Jong-un, and the North's test of a medium-range missile in February.