The South Korean military has been put on high alert on the western border in order to respond to North Korea's actions even as the government in Seoul demanded an apology from Pyongyang for the recent explosion in the demilitarised zone (DMZ).

The move came shortly after South Korea resumed its loudspeaker campaign in the western front-line area to warn North Korean soldiers.

"The top-notch alert was issued after resuming the loudspeaker broadcasting in the centre-to-western front-line area after 5:00 p.m. yesterday (10 August). 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," a South Korean official with the ministry of national defence told Seoul's Yonhap news agency.

The explosion on the southern side of the heavily-fortified DMZ injured two South Korean soldiers. An investigation into the incident by the South Korean military claimed North Korean troops had planted the landmines, which caused the blast. The UN Command has also condemned Pyongyang for the act.

"We urge North Korea to offer an apology over the provocation and punish those responsible for it," said South Korea's presidential spokesperson Min Kyung-wook.

In a statement released by the UN, Secretary-General Ban Ki-moon also called on Pyongyang to "fully adhere to the obligations under the Armistice Agreement and engage in dialogue on this incident".