The United States has started shipping an anti-missile system to South Korea after North Korea tested medium-range missiles Monday, according to a new report.

The platform’s presence in South Korea is controversial, as China fiercely opposes its deployment there, NBC News said Monday.

The Terminal High Altitude Area Defense system (THADD) is specifically designed for threats like North Korea, and the system already has active platforms in Guam and Hawaii focused on threats from Pyongyang.

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U.S. officials told NBC the “first elements” of a THAAD installation have already arrived in South Korea, hours after its acting president and prime minister begged for a deployment as quickly as possible there.

Prime Minister Hwang Kyo-ahn said the consequences of North Korea possessing a nuclear arsenal would be “horrible and beyond imagination.”

Defense officials stressed that THAAD is “strictly a defensive system” aimed at defending South Korea against North Korean missiles.

A THAAD deployment in South Korea was already in the works before North Korea’s latest missile test, they added, noting the timeline for the system's presence in the former was not changed by the latter's experiments.

The U.S. and South Korea first announced the deployment of a THAAD system last July, a move which drew quick condemnation from China.

China’s state-run media blasted the decision, with one outlet, China Daily, saying the “negative influence of the deployment of THAAD ... is similar to that of the Cuban Missile Crisis."

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North Korea test fired four missiles into the Sea of Japan on Monday, a move seen as a provocation of Japan and South Korea.

White House press secretary Sean Spicer condemned the launches that afternoon, arguing they are “consistent with North Korea’s long history of provocative behavior.”

“The United States stands with our allies in the face of this very serious threat,” he said during his daily briefing.

“The Trump administration is taking steps to enhance our ability to defend against North Korea’s ballistic missiles,” Spicer added, citing the THAAD deployment in South Korea.

Former President Barack Obama Barack Hussein ObamaGOP senator blocks Schumer resolution aimed at Biden probe as tensions run high D-Day for Trump: September 29 Obama says making a voting plan is part of 'how to quarantine successfully' MORE reportedly warned President Trump that North Korea would be “the most urgent problem” the latter faces in office.

North Korea said in September it had conducted a nuclear test, and the reclusive Asian nation has also promised to create its own intercontinental ballistic missiles.