North Korea reportedly deployed anti-aircraft artillery near the inter-Korean Military Demarcation Line after a defectors' group in South Korea claimed last month that it sent anti-Pyongyang leaflets across the border.

Fighters for a Free North Korea said on April 30 that it sent large balloons carrying around 500-thousand leaflets and unveiled video footage.

Police have been looking into the claim and it is believed that some of the leaflets did make it over the border and were collected by the North.

Deployment of anti-aircraft artillery was detected afterwards, implying that the leaflet incident was likely reported to North Korean leaders.

In fact on May 2, North Korean leader Kim Jong-un's sister Kim Yo-jong slammed leaflet circulation as an "intolerable provocation" and warned of "corresponding action."

Pyongyang's seemingly sensitive reaction is believed to also relate to antivirus efforts as state media recently warned that COVID-19 could make it into the country through objects carried by the wind.

The South Korean military and government are keeping tabs on the situation while President Moon Jae-in stressed stern law enforcement regarding leaflet campaigns.