North Korea is rebuilding guard posts and bringing large weaponry inside the demilitarized zone (DMZ), South Korea’s Defense Ministry said Monday, four days after the regime declared it would no longer abide by an inter-Korean military pact designed to reduce tensions along the border.

Defense Ministry officials disclosed photos showing North Korean soldiers building makeshift watch towers and carrying large firearms into the DMZ.

The North said on Thursday that it would restart all military activities that it had suspended under the 2018 inter-Korean military agreement.

South Korea had earlier said it would resume surveillance and reconnaissance activities along the border in response to the North’s launch of a spy satellite on Nov. 21.

The South Korean Joint Chiefs of Staff (JCS) and National Intelligence Service (NIS) have said that the North Korean satellite entered a regular orbit after its launch.

While Seoul and Washington have condemned the satellite launch as a violation of multiple United Nations Security Council resolutions that ban Pyongyang from conducting tests of ballistic missile technology, the regime has defended the launch as a  “legitimate exercise” of its right to strengthen its “self-defensive capabilities,” according to the North’s state-controlled Korean Central News Agency.

According to a senior South Korean military official who spoke to reporters on condition of anonymity, only a few guard posts are currently being rebuilt, but the North “is expected to restore all of them as they are essential facilities for surveillance.”

The South Korean military began observing heightened North Korean activity at the border on a Friday, a day after the North vowed it would “never again be bound” by the military pact.

The agreement, which was signed by then-South Korean President Moon Jae-in and North Korean leader Kim Jong-un, entailed the demolition of guard posts on both sides within 1 kilometer (0.62 miles) of the military demarcation line and a ban on military exercises and surveillance flights near the border to reduce the risk of accidental clashes.

Each side demolished ten guard posts after the agreement was signed.

South Korea’s Defense Ministry said it would closely watch North Korean activities along the border.

“Our military will closely monitor North Korean provocations while maintaining full readiness to retaliate immediately and forcefully with close cooperation with the United States,” the ministry said.

JCS Chairman Gen. Kim Myung-soo said Seoul’s military will undertake “corresponding measures” against Pyongyang’s latest act.

“It all depends on the enemy’s behavior,” he told reporters on Monday.

“North Korea is the one that has broken trust,” he said, adding that inaction by South Korea “would be more foolish.”

President Yoon Suk Yeol’s office said he received a full report from Defense Minister Shin Won-sik and Kim upon his return to Korea on Monday.

According to the presidential office, Yoon told both that the South Korean military “should ceaselessly monitor the North’s activities and maintain steadfast readiness so that the people can feel secure.”

BY MICHAEL LEE [lee.junhyuk@joongang.co.kr]