South Korean presidential candidate Yoon Suk-yeol’s visit to a front-line division in the Demilitarized Zone has come under fire, with the United Nations Command officially kicking off an investigation into an alleged violation of the Armistice Agreement.

The UNC made an announcement after Yoon -- dressed in a military uniform -- on Monday visited the observation post of the South Korean Army’s 3rd Infantry Division, also known as the Baekgol Unit, in the DMZ.

In what appears to be a rare move, the UNC publicly said it had begun an investigation into unauthorized activities taking place at OP 241 Baekgol. 

The UNC did not specify the names of people under investigation in the statement, which was originally issued Tuesday and disclosed to the public Wednesday. The UNC had taken the statement down from the official website as of Thursday noon, without further explanation.

“The UNC Commander has initiated an investigation into the incident to determine the root cause of failure and ensure there is neither a repetition of actions that undermine compliance with the terms of the Korean Armistice Agreement nor actions that put civilians under greater risk than is absolutely necessary,” the statement read.

The UNC listed several acts as noncompliance of the Armistice Agreement, including the use of military attire and authorizing additional personnel into the DMZ without the UNC’s approval.

In the statement, the UNC also took issue with Yoon and other visitors being allowed “access outside of specially designated and controlled areas designed to minimize the potential for threats to civilians.”

The UNC said it would take actions “as appropriate under the Armistice and standing agreements” with the South Korean government.

Some facilities at the Baekgol Unit are located within the areas controlled by the UNC, which extends 2 kilometers outward of the Military Demarcation Line.

The main mission of the UNC is to maintain and enforce the 1953 Korean Armistice Agreement. The UNC is responsible for investigating the violation of armistice rules, but the UNC does not disclose all the cases under scrutiny in general.

In response, Yoon’s presidential campaign said his visit to the observation post was conducted with the permission of the Ministry of National Defense. Yoon’s camp added that the candidate donned the military uniform under the guidance of the Baekgol Unit.

South Korea’s Defense Ministry on Thursday said the military is looking into the case and added that it would consult with the UNC over several issues, including the outfit of civilians during their visit to the DMZ.

This is not the first time that a politician’s visit to the DMZ has caused trouble.

South Korea’s Defense Ministry previously sent an official letter to political parties to ask them to refrain from visiting military units in the runup to the 2017 presidential election. The ministry reportedly sent the letter in a bid to maintain political neutrality and to avoid adding any unnecessary burden on soldiers.

Critics said although the presidential candidates’ visits to military units are symbolic in nature, they do send a political message.

Political commentator Rhee Jong-hoon said South Korean presidential candidates’ visits to military units are more of a “compulsory course” in light of the significance of security issues on the Korean Peninsula.

“Their visit will not draw more public attention. But they will face inevitable public criticism if they do not visit troops.”

Eom Gyeong-yeong, director of the Zeitgeist Institute, said presidential candidates have sent a “strong message” to the public and demonstrated their emphasis on national security issues by visiting military units.

Considering the inclination of conservative voters to put priority on national security policy, the presidential candidate of an opposition party would see the usefulness of the visit.

“A visit is intended to rally conservative voters,” Eom said. “But on the other hand, presidential candidates visit (military units) habitually, rather than being based on political considerations and calculations.”

Others said South Korean military authorities should stop indiscreetly allowing politicians and presidential candidates to visit front-line units in the DMZ in what they said repeatedly violates and undermines the Armistice Agreement.

South Korea’s Defense Minister Suh Wook this month underscored the importance of “strictly maintaining political neutrality” during the meeting of top commanders from the Army, Air Force, Navy and Marine Corps.