"We once again warn the enemies that it is the steadfast will of the Korean People's Army to make merciless retaliatory strikes to reduce South Korea to a sea of flames and debris once an order is issued," the military's artillery bureau was quoted as saying by the KCNA.

It marked the communist country's first reaction to the allies' decision reached on Friday to set up the system in South Korea, where about 28,500 American troops are stationed.

South Korea's defense ministry immediately hit back at the North's threat.

"North Korea needs to clearly see who is responsible for putting the Korean Peninsula's peace and security at risk before criticizing the THAAD deployment decision," Moon Sang-gyun, spokesman at the Ministry of National Defense, said in a briefing.

"If North Korea continues its groundless claims and rash actions in defiance of our warnings, it will have to face our military's stringent retaliation," he noted.

The defense ministry is expected to announce the site for the deployment within a few weeks.

The deployment is aimed at countering the North's evolving missile threats amid concerns about the technical progress of North Korea's nuclear and missile programs.

Last month, the communist regime claimed the successful launch of an intermediate-range ballistic missile, saying it has the capacity to strike U.S. forces in the Pacific region.

On Saturday, the North test-fired a submarine-launched ballistic missile (SLBM) off its east coast, marking the fifth attempt since last May, according to the South Korean military.

The country's SLBM launches have not been successful so far, but experts said if North Korea accomplishes technical advances, the missiles could serve as a fresh threat to regional security.

It is very difficult to counter submarine launched ballistic missiles, although South Korean Defense Minister Han Min-koo on Sunday said the THAAD system will be capable of intercepting such a threat.

China and Russia have explicitly expressed opposition against the THAAD deployment in South Korea on concerns that the move could hurt their strategic security interests.

Beijing claims that the system can be used against it on concerns that the powerful X-band radar that comes with THAAD could spy on China's military. Washington said that THAAD is a purely defensive system aimed only at North Korea's evolving threats.

In March, the U.N. Security Council imposed its toughest sanctions to date on North Korea for its fourth nuclear test and long-range rocket launch in the following month.

The United States has maintained a significant troop presence in South Korea following the Korean War (1950-53), which ended in a truce, not a peace treaty, leaving the divided peninsula still technically at war. (Yonhap)