The US has reportedly installed four additional launchers of the Terminal High-Altitude Area Defense (THAAD) system in South Korea.
The deployment has been completed a month after South Korean President Moon Jae-in decided to resume deliveries of additional THAAD launchers.
In June, Jae-in announced his decision to temporarily suspend the deployment of the THAAD system in the country until an environmental impact assessment had been completed.
The suspension halted the installation of the four additional launchers.
Nearly 400 protesters arrived at a former golf course, where the latest THAAD launchers are installed, Associated Press reported.
South Korea has deployed thousands of police personnel to ensure safe delivery and installation of the equipment.
South Korea Prime Minister Lee Nak-yon said that North Korea may launch an intercontinental ballistic missile (ICBM) on 9 September.
Nak-yon was quoted by CNN as saying: "The situation is very grave. It doesn't seem much time is left before North Korea achieves its complete nuclear armament.
"A special measure is urgently needed to stop their recklessness."
Japanese Prime Minister Shinzo Abe and South Korea President Moon Jae-in stated: "Now is the time to further increase sanctions and pressures against the North as much as possible rather than seeking dialogue.”