"Considering the gravity of the matter, we have decided to file the complaint against the official for leaking the classified information, and Rep. Khang for being the direct cause," the foreign ministry said in a statement to the media as quoted by Yonhap.
The diplomat in question had no clearance to access confidential information, which can be accessed only by South Korean Ambassador Cho Yoon-je and several other senior South Korean officials, the agency noted.
He reportedly obtained the information from his colleague at the embassy, who is now also facing a reprimand.
In a statement released by his lawyer, the diplomat acknowledged the wrongdoing but said he had shared a confidential information at the insistence of Khang, who said he would use it only for a background reference, according to Yonhap.
White House spokesperson Judd Deere said in a statement on May 7 that the talks between Trump and Moon focused on recent developments regarding North Korea and ways to achieve its full denuclearization.