Seoul (CNN) South Korea's new government has suspended the deployment of a controversial US missile defense system that strained relations with China and angered North Korea.

An official told CNN on Wednesday that while Seoul will not withdraw two launchers of the Terminal High Altitude Area Defense (THAAD) system that are already in action, four additional launchers will not be deployed until "a full-blown environmental impact assessment is completed."

During the recent election campaign, South Korean President Moon Jae-in called for the THAAD rollout to be halted and any decision about its future to be put before the country's parliament.

Deployment of THAAD was agreed by his predecessor -- disgraced President Park Geun-hye -- and Washington. The system was declared partially operational a week before Moon was elected.

At the time, analysts said this was an attempt to force Moon's hand and make it difficult for his government to withdraw the system from South Korea.

The THAAD rollout has been vociferously opposed by China, which fears it could be used to spy on its own defense and nuclear deterrent systems.

Relations between Seoul and Beijing have soured significantly as a result of its deployment, affecting South Korean businesses and Koreans living in China

A spokesman for the Pentagon said the United States will work with the South Korean government "throughout this process."

"The US trusts (South Korea's) stance that the THAAD deployment was an alliance decision and it will not be reversed," Navy Cmdr. Gary Ross said.

Gen. Mark Milley, US Army chief of staff, told the Senate Subcommittee on Defense that the system is essential to protect thousands of US troops in South Korea, as well as South Korean citizens.

"We'll work through it, and at the end of the day I think the Republic of Korea will be properly supported by the United States," he said.

Delayed deployment

THAAD was not due to be fully operational until the end of the year. The environmental assessment -- even if it ultimately permits deployment to continue -- will likely delay this to at least 2018.

The system is designed to shoot down short- and medium-range ballistic missiles in the latter stages of their flight as they plunge toward their targets.

While this means it cannot act against the type of intermediate-range missiles North Korea has been testing in recent months, THAAD also includes a sophisticated radar that will fit into an overlapping series of US missile defense systems, including Aegis warships operating in the Pacific and Patriot missile batteries deployed in Japan.

The radar could provide critical early tracking data to these missile interception systems, as well as those protecting Guam, the closest US territory to North Korea.