The South Korean ministry in charge of inter-Korean affairs has assessed that it's very unusual for North Korea to release images of burning anti-Pyongyang leaflets sent by defector groups in the South.

At a press briefing on Monday, unification ministry spokesperson Koo Byoung-sam called North Korea's recent move to be unprecedented, and that the ministry will look into the regime's intent.

The spokesperson added that Seoul had declared to take steps that would be "unbearable" for Pyongyang, should it continue its irrational and vulgar provocation of sending trash-carrying balloons to South Korea.

When asked about Seoul proactively restricting the leaflet activity amid the inter-Korean confrontation, the spokesperson said the government is approaching the issue in consideration of the Constitutional Court's decision to guarantee freedom of expression.

In a statement on Sunday, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, said she was informed about the discovery of "dirty leaflets and items" from South Korea in the North's border area and elsewhere.

Kim said the leaflets and items have been incinerated, revealing two photos showing what seemed to be the leaflets dropped in North Korea, and authorities burning the leaflets and items assumed to be cold medicine.