Washington, Seoul's key security ally, stations about 28,500 troops and a range of air and missile defence systems in the South to help deter aggression from the nuclear?armed North.

The Washington Post reported this week that the United States was moving parts of its Terminal High Altitude Area Defence (THAAD) system from South Korea to the Middle East, citing unnamed officials.

"Regardless of whether certain USFK assets are deployed overseas, there is no issue whatsoever with our deterrence posture against North Korea, given the level of our military capabilities," the defence ministry said in a statement to AFP on Wednesday, referring to the United States Forces Korea command.

It declined to confirm the report.

The THAAD missile defence system is designed to intercept short, medium and intermediate?range ballistic missiles using hit?to?kill technology.

It was installed in South Korea in 2017, a move that sparked strong protests from China.

President Lee Jae Myung has said his government is unhappy with the reported asset move but acknowledged there was little it could do about it.

"The government is opposing the USFK's withdrawal of some air defence weapons for its own military needs," he said on Tuesday.

"But the stark reality is that we are unable to fully implement our opinions."

A photo taken by Yonhap news agency last week and released on Tuesday appeared to show parts of the THAAD battery being dismantled in Seongju County, about 220 kilometres (136 miles) south of Seoul.

A presidential official told AFP it was "inappropriate" to comment on questions regarding any military asset redeployment and cautioned against media speculation.

"Speculative reports on militarily sensitive matters are undesirable in light of our security interests... and our relations with key Middle Eastern countries," he said.