South Korea says that North Korea has exploded an inter-Korean liaison office building—a de facto joint embassy designed to help the two countries communicate—just north of the Korean border. North Korea had previously threatened to destroy the building after becoming incensed by Seoul’s failure to stop activists from flying propaganda leaflets across the border. The site was opened in 2018 to help the two Koreas solve problems through diplomacy, but has been empty since January due to COVID-19 restrictions. Seoul’s Unification Ministry said the destruction of the building at the North Korean border town of Kaesong happened Tuesday afternoon local time. Earlier in the day, North Korea’s army warned it is ready to enter the demilitarized zone dividing the two Koreas and, over the weekend, Kim Yo Jong, the sister of North Korean leader Kim Jong Un, said she’d ordered the army to prepare for the invasion.