The United States has reportedly started the deployment of the Terminal High Altitude Area Defense (THAAD) anti-ballistic missile system in South Korea.
The country's defense ministry said that parts of the system were delivered on Monday to the Osan Air Base in Pyeongtaek, 43 miles south of Seoul.
"[The government] has completely disregarded public calls and demands from political circles with regard to the THAAD deployment," spokesman for the Democratic Party Youn Kwan-suk said.
The government made a decision unilaterally and did not get the public approval, he said, Sputnik reported.
"From the clandestine push for the deployment to the process of making the final decision on the installation, the government has unilaterally pressed ahead with it without any consultations with citizens," Youn added.
The People’s Party also condemned the THAAD installation, saying the move must be approved by the parliament.
Seoul and Washington agreed to deploy the THAAD system, designed to intercept short, medium and intermediate ballistic missiles at the terminal incoming stage, in July 2016, amid South Korea's growing unease about Pyongyang's nuclear program.