SEOUL, South Korea (AP) — North Korea is restoring front-line guard posts that it had dismantled during a previous period of inter-Korean rapprochement, South Korea’s military said Monday, after animosities spiked between the rivals over the North’s recent spy satellite launch.

The two Koreas previously dismantled or disarmed 11 of their guard posts inside their heavily fortified border, called the Demilitarized Zone, under a 2018 deal meant to ease front-line military confrontations. But the deal is now in danger of being scrapped as both Koreas openly threaten to breach it.

The 2018 agreement required the two Koreas to halt aerial surveillance and live-fire exercises at no-fly and buffer zones that they established along the DMZ, as well as remove some of their front-line guard posts and land mines. The deal left South Korea with 50 board guard posts and North Korea with 150.

After North Korea claimed to place its first military spy satellite into orbit on Nov. 21, South Korea said it would partially suspend the deal and resume aerial surveillance along the DMZ in response. South Korea said its response was “a minimum defensive measure” because the launch showed the North’s intentions to strengthen its monitoring of the South and improve its missile technology.

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North Korea immediately slammed South Korea’s decision, saying it would deploy powerful weapons at the border in a tit-for-tat measure. The North said it also won’t abide by the 2018 deal any longer.

South Korea’s Defense Ministry said in a statement Monday that it detected North Korea building guard posts at border sites where its dismantled guard posts once stood, and that North Korea deployed troops and heavy weapons there.

The ministry distributed to media outlets photos of North Korean soldiers building a guard post and moving a suspected recoilless rifle to a newly built trench.

South Korean President Yoon Suk Yeol ordered the military to keep a close watch on the North and maintain a firm readiness, according to his office. The South Korean Defense Ministry later said it’s ready to “promptly and strongly punish” North Korea over any provocation that it launches.

South Korea, the United States and others strongly condemned the North’s satellite launch, which they viewed as a provocation that threatens regional peace. United Nations Security Council resolutions ban any satellite launches by North Korea because the world body regards them as covers for testing its long-range missile technology. North Korea says it has sovereign rights to launch spy satellites to cope with what it says are escalating U.S.-led military threats.

On Monday, Kim Son Gyong, a senior North Korean Foreign Ministry official, called the U.S. and others’ condemnation of the satellite launch “a typical expression of the most hideous and brazen-faced violation of sovereignty that denies the justification of the existence” of North Korea.

South Korean officials said they confirmed the North Korean satellite entered orbit. But they said they need more time to verify whether the satellite is functioning normally.

North Korea’s state media said Monday that leader Kim Jong Un was shown pictures taken by the spy satellite of a military facility in the U.S. Pacific territory of Guam. State media earlier said Kim had been presented with satellite photos of U.S. military bases in Hawaii and key sites in South Korea. North Korea hasn’t released those satellite images.

Kim previously said the satellite gives North Korea “eyes overlooking a very long distance and a strong fist beating a very long distance.”

Many experts doubt the satellite’s ability to take high-resolution images, though they said it would still be militarily useful for the North.

South Korea suspects Russian technological assistance likely enabled North Korea to send the spy satellite into space. South Korean, U.S. and Japanese officials accused North Korea of seeking high-tech Russian technologies to enhance its military programs in return for shipping conventional arms to support Russia’s war in Ukraine. Both Russia and North Korea denied the alleged weapons transfer deal.