North Korea has started to restore guard posts within the demilitarized zone, which had previously been demolished in accordance with the 2018 inter-Korean military agreement while bringing military personnel and firearm equipment back to the posts, Seoul said Monday.

Movements to restore the military posts have been detected since Nov. 24, one day after North Korea declared a complete annulment of the Sept. 19 military agreement, the Defense Ministry in Seoul said in a statement.

South Korea's Defense Ministry also released photos captured by ground-based surveillance equipment, including thermal observation devices, that show the activities of the North Korean military in the eastern region near the inter-Korean border.

Seoul has observed that Pyongyang has deployed its military personnel and heavy firearms, and is constructing observation posts atop of formerly demolished guard posts, in an apparent attempt to restore the 11 guard posts.

In 2018, as part of the Sept. 19 Comprehensive Military Agreement, South and North Korea dismantled 10 guard posts located within 1 kilometer of each other in the DMZ, covering the eastern, western and midland regions. While one guard post, acknowledged for its historical significance, was preserved from each side, the withdrawal of all military personnel and equipment from the guard posts took place.

"There have been sporadic military activities at certain previously destroyed guard posts (since 2018). However, activities such as the construction of observation posts, importing heavy firearms or engaging in continuous day and night border surveillance, as is currently being observed, had not been observed," a senior military official told reporters on condition of anonymity.

The images depict North Korean soldiers constructing a wooden observation post atop the previously demolished guard post. Additionally, they show the soldiers applying camouflage patterns to the observation post.

Another photo showcases North Korean soldiers transporting firefighting equipment, including what seems to be a recoilless rifle, subsequent to constructing military encampments near a guard post that had been demolished. The last image, taken by thermal imaging, depicts North Korean soldiers performing guard shifts during the night.

"As it is an ongoing process, only a few locations for building observation posts exist at the moment. However, I anticipate that all observation posts will likely be constructed, given their essential role in surveillance. Subsequently, I expect the establishment of military encampments in areas near the guard posts," the official said.

"Furthermore, reflecting on the past, there were facilities not only in the front but also in the rear. These facilities may include their own barracks or similar structures. I speculate that with sufficient time, these facilities will likely undergo a gradual restoration process," the official continued.

North Korea's Defense Ministry pledged to retract all military measures designed for tension reduction and prevention of inadvertent conflicts on the ground, at sea, and in the air. Instead, they vowed to "forward-deploy more powerful armed forces and new-type military equipment along the military demarcation line."

North Korea's decision came in response to South Korea's announcement one day before on Nov. 22, that it was suspending part of the 2018 Comprehensive Military Agreement, specifically the no-fly zone clause. The developments followed a spy satellite launch by North Korea on Nov. 21.

"The ultimate intention appears to be a part of the annulment process, as the country has recently announced its withdrawal from the Sept. 19 agreement," the official said.

Another military official said the South Korean military is "currently thoroughly monitoring the enemy movements and conducting search and ambush operations in the areas where South Korea has withdrawn its guard posts." The military is keeping close tabs on "potential provocations" by North Korea.

The South Korean military has detected a surge in the number of gates opening up at coastal artillery bases, increasing from one or two in the past to over 10 at present, an unnamed official from the Defense Ministry said. Each base is equipped with two coastal artillery units.

In the Sept. 19 military agreement, the two Koreas had agreed to install covers on the barrels of coastal artilleries and ship guns as well as close all gunports in the maritime buffer zone.

President Yoon Suk Yeol was briefed by Defense Minister Shin Won-sik and Chairman of the Joint Chiefs of Staff Gen. Kim Myung-soo on Monday after he returned from France and the United Kingdom, presidential spokesperson Lee Do-woon said.

The president has instructed to maintain a firm military readiness posture and to meticulously monitor North Korea's movements, so as to ensure people feel safe, according to Lee.

Gen. Kim, who assumed office last Saturday, said Monday that the South Korean military will take "corresponding measures" in response to North Korea's decision to restore guard posts.

"North Korea is the one that has shattered our trust, so time will reveal the nature of the countermeasures we will adopt. We must implement fundamental measures to maintain our readiness posture," Kim told reporters. "The decision not to take any countermeasures appears more foolish."