The court also said that the US and South Korea formed the task force to discuss the issue on condition that their discussions remain confidential and that members of the team signed a confidentiality agreement.

"The information requested by the plaintiff is classified as second-degree secret and includes the detailed scope and capability of THAAD, as well as simulation analysis of candidate sites and the outcome of site surveys," the court said.

"If this is disclosed, North Korea or a third country could obtain the defense scope and capability of THAAD, as well as information on deployment status, and could use the information to evade THAAD's missile defense capabilities," it said.

The court also said that the South's unilateral disclosure of such information could have negative effects on the alliance with the US and impair trust between the two countries. (Yonhap)