North Korea issued a warning to South Korea that it would take measures to completely isolate its territory from the south, and blew up two main roads that connected to the southern region of the peninsula on Tuesday, South Korean officials said, as reported by CNN.

Seoul’s Joint Chiefs of Staff (JCS) said North Korea detonated explosive devices on two major road and railway links around 12 pm, prompting the South Korean military to open fire.

The South Korean Defense Ministry released a video that depicted numerous explosions on roadways located on the northern side of the military demarcation line that divides the two Koreas. The video shows that heavy machinery, such as trucks and excavators, were deployed to at least one of the roads, which was partially obstructed by a black barrier, according to the network. The JCS stated that the North was performing “additional works with heavy machinery” at the location, but it did not provide any detailed information.

South Korea said they opened fire towards the demarcation line as a defense mechanism, explaining that their forces have maintained “readiness posture under cooperation with the US.”

The two Koreas remain divided by one of the world's most heavily fortified borders, and the impacted roads have not been in use for years. The move by North Korea comes at a time of increased political tension by the Kim Jong Un regime against their neighbors to the south.

South Korean officials announced on Monday that it had identified indications that North Korea was preparing to demolish the highways that connect the two countries, cautioning that the explosions could occur at any moment. The Defense Ministry stated that its military had implemented countermeasures, but it did not provide any specifics.

North Korea accused South Korea of flying propaganda-filled drones over its capital, Pyongyang, and threatened “retaliation” a few days prior to the blasts. After North Korean leader Kim Jong Un abandoned a longstanding policy of pursuing peaceful reunification with the South earlier this year, the North Korean army issued a warning last week that it would take the “substantial military step” of completely isolating its territory from South Korea.