North Korea’s military Tuesday issued an “ultimatum” saying it would attack without warning if anti-North Korean activities continued in the South.

The warning came after protestors in Seoul on Monday burned portraits of North Korea’s founder Kim Il-Sung, his son Kim Jong-Il and grandson and current leader Kim Jong-Un.

The act coincided with national celebrations in North Korea for the 101st anniversary of the birth of Kim Il-Sung, a day it reveres as “The Day of the Sun”.

“All the service personnel and people of the DPRK (North Korea) are simmering with towering resentment at this monstrous criminal act,” the army’s supreme command said in a release carried on the official Korean Central News Agency.

In an “ultimatum” to the South, it warned: “Our retaliatory action will start without any notice from now as such a thrice-cursed criminal act of hurting the dignity of the supreme leadership of the DPRK is being openly committed in the heart of Seoul under the patronage of the puppet authorities.”