In a sign of North Korea’s unwavering stance, the regime’s military has once again delivered threats of retaliation against South Korea following “atrocious” anti-Pyongyang protests in Seoul.

The Korean People’s Army slammed the burning of portraits of North Korea’s founder Kim Il-Sung, his son Kim Jong-Il and young leader Kim Jong-un in Seoul on Monday, saying it was an “unforgivable” and “monstrous criminal act”, Yonhap News Agency reports.

“The supreme command of the Korean People’s Army Tuesday issued an ultimatum to the South Korean puppet group,” the army’s supreme command said in a statement carried by Pyongyang’s official news agency KCNA.

“Our retaliatory action will start without any notice from now as much as such 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,” the army said.

The protests coincided with the 101st birth anniversary of the North’s founding leader, Kim Il-sung, amid speculations it would test-fire a medium-range missile to mark the national celebration, reports AFP.

Pyongyang rejected an inter-Korean dialogue and said Seoul should apologize for all of its anti-North Korean acts.

North’s latest threat came on the heels of US Secretary of State John Kerry’s tour around Asia in a bid to defuse tensions on the Korean peninsula. Kerry said he was willing to reach out to the isolated nation if it signals a move to dismantle its nuclear weapons arsenal.