North Korea on Wednesday said it conducted its recent missile launch drill with the aim of practicing pre-emptive strikes against South Korean ports and airfields.

On Tuesday, Pyongyang test-fired three ballistic missiles -- two Scuds and one Rodong -- in an apparent "armed protest" against South Korea's decision early this month to deploy an advanced U.S. anti-missile system in the country to counter growing threats from the North.

"The drill was conducted by limiting the firing range under the simulated conditions of making pre-emptive strikes at ports and airfields in the operational theater in South Korea, where the U.S. imperialists' nuclear war hardware is to be hurled," North Korea said in an English dispatch carried by the Korean Central News Agency.

North Korean leader Kim Jong-un "provided field guidance to the drill," observing that the ballistic missiles launched in Hwangju, North Hwanghae Province, flew across the country and hit the East Sea, the KCNA said.

In the "successful" drill, the KCNA said North Korea "once again examined the operational features of the detonating devices for nuclear warheads mounted on the ballistic rockets at the designated altitude over the target area."

A day after the North's latest saber rattling, the Rodong Sinmun, the North's main newspaper, carried a total of eight photos related to the missile launches on its front page. The photos include one showing a smiling Kim Jong-eun satisfied with the test results, while others showed the three rockets being launched.

A photo also showed a large map covering a desk that displayed the possible flight path of the missiles from Hwangju to areas near South Korea's southern port cities of Ulsan and Busan.

Meanwhile, the Panmunjom Mission of the Korean People's Army said in a statement that the U.S. military forces in South Korea will be the first targets in any attack and this will be followed by the South Korean "puppet" troops.

A KPA spokesman strongly condemned the U.S. for holding operational control over South Korean forces in the event of war breaking out. Washington has held OPCON for the past 66 years since 1950 when the three-year Korean War started.

"In case the U.S. imperialists transfer OPCON to the puppet forces, they will lose not only the pretext for staying in South Korea but also the excuse for interfering in Korean issues," the spokesman said.

South Korea regained peacetime operational control of its forces from the U.S. in 1994 during the Kim Young-sam administration.

In 2014, Seoul and Washington agreed in their Security Consultative Meeting, to delay the OPCON transfer, previously set for late 2015, until South Korea gains full defense capabilities.

The timing is estimated to be around mid-2020 when South Korea will have finished the installation of its locally produced defense systems like its "kill chain" and Korean Air and Missile Defense. The kill chain aims to enhance Seoul's capability to detect and destroy North Korea's weapons of mass destruction.

On July 8, Seoul and Washington agreed to deploy the Terminal High-Altitude Area Defense system in South Korea by the end of 2017 to deal with evolving nuclear and missile threats from the North. (Yonhap)