New President Moon Jae-in suspended THAAD's deployment shortly after taking office but reversed that decision as the North conducted increasingly advanced missile tests and rebuffed his efforts to pursue dialogue.
South Korea's defense ministry had said Monday the remaining THAAD launchers would be installed quickly to respond to "North Korea's advancing nuclear and missile threats".
China and Russian Federation have advocated a "freeze for freeze" plan, under which the United States and South Korea would stop major military exercises in exchange for North Korea halting its weapons programmes. He said there are "many reasonable people in the current administration" who are experienced and who have dealt with similar crises.
Mr Moon and Mr Abe agreed to co-operate on seeking tougher United Nations sanctions against North Korea and pledged to strengthen efforts to persuade Beijing and Moscow to cut off oil supplies to the North, said Mr Moon's press secretary. Putin said North Koreans would "eat grass" rather than give in to outside pressure to disarm.
Chinese foreign ministry spokesman Geng Shuang reiterated Beijing's opposition to South Korea's deployment of the Terminal High-Altitude Area Defense System, also known as THAAD.
Russian Federation and China are concerned over the deployment of these systems in the area.
China is a veto-wielding permanent member of the U.N. Security Council, as well as North Korea's main trading partner and source of food and fuel aid.
Local residents have fiercely protested it, claiming the former Park Geun-hye administration made a hasty decision on the deployment of the U.S. weapon system without the due domestic procedures.
South Korea's air force and army conducted exercises involving long-range air-to-surface and ballistic missiles on Monday, the joint chiefs of staff said, adding more drills were being prepared with USA forces in the South.
Local newspaper Kukmin Ilbo reported Wednesday a total of six civic groups opposing THAAD have gathered, and the usual force of 200 conscripted police have been replaced by 360 regular police officers. The launchers were transported to the site by some 10 United States military vehicles from the Osan Air Base near Seoul.
Seoul's Defense Ministry later confirmed the deployment, but stated the launchers will only stay permanently in South Korea if the system passes a thorough environmental impact examination.
Washington and Seoul began deploying THAAD before a conservative South Korean government was ousted in March in a corruption scandal.
The four launchers, support vehicles and construction equipment started rolling by overland route from Camp Carroll in Waegwan, North Gyeongsang Province at dead of night.
Moon said the installment could be completed at least on a temporary basis pending a full environmental assessment of the site. Two launchers had already been deployed.