The US Forces Korea (USFK) took key electronic equipment out of its THAAD missile defense base in South Korea on Monday after replacement equipment was brought into the base last month, officials said.

On May 29, the US military, with the assistance of the South Korean defense ministry, brought new interceptor missiles and other military hardware and equipment onto its Terminal High Altitude Area Defense (THAAD) base in the central town of Seongju by ground as replacements.

"Early today, the old Electronics Equipment Unit (EEU) was taken out of the base, as it took some time to transfer data to the new one and carry out tests," a defense ministry official said.

Most of the old equipment was moved out of the base in May, and other equipment for base construction will be taken out once related projects are completed, he added.

As for criticism of their launching of the ground transport operations without prior notice, the official said it aims to minimize friction with local residents, stressing that the authorities took and will take necessary steps to ensure public safety over the course of those movements.

Some local residents and civic activists have tried to block new equipment and other supplies from entering the base, forcing the US military to use air transportation to move supplies.

"The equipment brought in last month is too heavy to be airlifted. We will continue to make efforts to fully discuss the issue with residents," the official noted.

The introduction of new THAAD equipment has sparked speculation, such as that the US might deploy additional launchers or move to upgrade the batteries. But the ministry flatly rejected it, saying such issues have never been discussed between Seoul and Washington.

As an integral part of the US-led missile-defense system, THAAD is designed to shoot down short-, medium- and intermediate-range ballistic missiles at a higher altitude in their terminal phase using a hit-to-kill method.

South Korea hosted the US battery in 2016, which led to strong opposition from China and its economic retaliatory measures.

Seoul and Washington have stressed that the system aims only to better cope with the growing missile threats posed by North Korea. (Yonhap)