Meanwhile, North Korea shows no signs of ending its nuclear and ballistic missile tests, calling its recent nuclear test and other "self-defense" measures a "gift package" for the U.S., warning that others are on the way if Washington continues its "reckless provocations".
With the four additional launchers installed, U.S. Forces Korea will have a fully operational THAAD battery at its base in Seongju.
CHINA has demanded an immediate stop to deployment of the Terminal High Altitude Area Defense (THAAD) system in South Korea.
The United States assured South Korea and Japan on Wednesday of full extended deterrence, based on both its conventional and nuclear arsenal, against North Korea.
Soon after Pyongyang launched another long-range missile July 28, South Korea President Moon Jae-in ordered the temporary deployment of additional THAAD launchers. There are now two launchers at the location.
China and Russian Federation have opposed the THAAD deployment - viewing it as aimed at bolstering Washington's military presence in the region.
South Korea's Defense Ministry has made a decision to temporarily install four additional launchers of the U.S. THAAD antimissile system on Thursday, making the six-launcher battery fully operational.
Trump's statement came after North Korea on Sunday detonated what it described as a hydrogen bomb designed for a long-range missile, sparking global alarm with what was by far its most powerful test to date.
Now, the missile defense system reliably closes the sky above South Korea.
The leaders of South Korea and Japan are holding talks with Putin in Vladivostok on the sidelines of a conference on economic development of Russia's Far East.