South Korea officially issued a full alert on its border following a mine explosion in the demilitarized zone (DMZ) that left two soldiers in critical condition. The country placed the responsibility on North Korea and demanded an apology although it has yet to hear back.

The move signals heightened military tensions between the North and South.

South Korea has resorted to means of non-violent retaliation, which includes playing South Korean news and anti-Pyongyang sentiments through military-grade loud speakers. In 2004, both countries agreed to stop these types of campaigns at the border, which included propaganda from the North. The communist country is known to keep a very tight leash on the types of information that gets propagated around the country.

But the South is also preparing for combat by further fortifying its borders.

“We can immediately retaliate in an emergency because we have stocked up our means of reconnaissance and artillery to monitor and retaliate against North Korea,” Defense Ministry Spokesman Kim Min-seok told reporters according to Yonhap.