WATCH: North Korea Blows Up Liaison Office It Shared With South Korea. North Threatens To Invade DMZ, South Goes To ‘Combat Control Office’.

North Korean officials blew up an office building on Tuesday that it used as place to work with South Korean officials, a move that experts say is a significant escalation between the two countries. The move comes after North Korea had threatened to invade the demilitarized zone with its military, and now the South has moved its joint chiefs of staff to a “combat control office.”

“South Korean border guards heard an explosion and then saw smoke rising from Kaesong, the North Korean town where the building was located,” The New York Times reported. “The building appeared to be blown completely apart in a blast so powerful that windows in nearby buildings were also shattered, according to video footage from a South Korean surveillance camera on the border.”