"President Moon said it was very shocking" to hear the four additional launchers had been installed without being reported to the new government or to the public, presidential spokesman Yoon Young-chan told a media briefing on Tuesday, Reuters reported.
The Terminal High Altitude Area Defense (THAAD) system battery was initially deployed in March in the southeastern region of Seongju with just two of its maximum load of six launchers to counter North Korean “missile threats.”
During his successful campaign for the May 9 presidential election, Moon called for a parliamentary review of the system, whose deployment has also infuriated China, North Korea's lone major ally.
Moon had campaigned on a more moderate approach to North Korea, calling for engagement even as Pyongyang pursues nuclear weapons and ballistic missile programs in defiance of UN Security Council resolutions and threats of more sanctions.
China tensions easing
Moon's order of a probe into the THAAD launchers came amid signs of easing tensions between major trading partners South Korea and China.
South Korea's Jeju Air said on Tuesday China has approved a plan to double its flights to the Chinese city of Weihai from June 2.
China has been incensed over the THAAD deployment, fearing it could give the US military the capability of seeing into its own missile systems, and could open the door to a wider deployment of the system, possibly in Japan and elsewhere.
China has denied it had discriminated against South Korean companies, which have faced product boycotts and bans on Chinese tourists visiting South Korea.
Although there have been no official orders from the Chinese government to lift the ban, a few Chinese travel agencies have sent inquiries about package tours, he said. However, Lotte Group has yet to reopen any of the 74 retail stores in China it was forced to close in March after the group allowed South Korea to install the THAAD system on land it owned.