South Korea has stationed tanks on the border with the North, threatening a strong reaction after Kim Jong-un's regime blew up an embassy building.
Tensions are high on the peninsula after the office - set up to encourage better relations between the neighbours - was "ruined" in a "terrific explosion".
It has led to fears of military clashes in the heavily guarded Demilitarised Zone (DMZ) that divides the neighbours, who are technically still at war, after the North said its troops were prepared to enter the area.
South Korean troops are amassing after the attack on the inter-Korea liaison office in the border town of Kaesong this morning.