"The conclusion of the small-scale environmental effect assessment and the initiation of temporary deployment are not in a cause-and-effect relationship. They will go separately," Moon Sang-gyun, a spokesman of the ministry, was quoted as saying by Yonhap News Agency.
The installation of four additional THAAD units will be implemented after consultations with the United States, the ministerial spokesman added.
In July 2016, following five months of negotiations, Seoul and Washington agreed on the deployment of THAAD units that might, where necessary, intercept ballistic missiles from North Korea. THAAD is designed to shoot down short, medium, and intermediate range ballistic missiles in their terminal phase.
On July 28, North Korea conducted its second intercontinental ballistic missile (ICBM) test. South Korean President Moon Jae-in stated that in response, South Korea would install additional THAAD launchers at a US military base in South Korea.