The South Korean military is keeping a close eye on military movements in North Korea after the North warned it would send propaganda leaflets in retaliation against defector-led anti-Pyongyang leaflet campaigns in the South.

Joint Chiefs of Staff(JCS) spokesperson Col. Kim Jun-rak said Monday that the military is monitoring the North around-the-clock and remains ready to respond to provocations.

Earlier in the day, the North's state-run Korean Central News Agency(KCNA) said it has printed 12 million propaganda leaflets to send south across the border through various means, including some three-thousand balloons.

North Korea did not specify when the leaflets will be sent, with some in the South suggesting it could be before or after the 70th anniversary of the outbreak of the Korean War on Thursday.

A military official said South Korea will have to opt for a military response if North uses an unmanned aerial vehicle or a drone.