Left-leaning Moon condemned the launch and joined calls for tighter sanctions on Pyongyang.
Seoul: Pyongyang warned it would be a "piece of cake" to destroy "gangster" South Korea, state media reported Thursday, as it raged against Seoul for a joint missile drill with the US following its landmark intercontinental ballistic missile (ICBM) test.
The isolated, nuclear-armed North sent a chill through the international community Tuesday after its missile launch, a milestone in Pyongyang's decades-long drive for the capability to threaten the US mainland with a nuclear strike.
US President Donald Trump had dismissed the idea of the North having a working ICBM, vowing it "won't happen," but experts say the missile could reach Alaska or even further towards the continental US.
The test prompted the US and the South to stage a joint missile drill aimed at countering the North's threats, after South Korean President Moon Jae-In called for a response beyond "just words".
North Korea hit back Thursday, with its propaganda National Peace Committee for Korea criticising Moon for denouncing Pyongyang "instead of getting rejoiced over the praiseworthy event" staged by its northern neighbour, according to the KCNA news agency.
Mocking the South as "puppet military gangsters," the KCNA report added: "It will be as easy as a piece of cake for the (North) to wipe out the puppet forces ... as we are now able to destroy even the US mainland across the ocean."
Left-leaning Moon, who has advocated dialogue with the North to bring it to negotiating table, condemned the launch and joined calls for tighter sanctions on Pyongyang.
The latest test drew also widespread condemnation and prompted the US to push for new, tougher sanctions against Pyongyang at an UN Security Council meeting held on Wednesday.
In a hard-hitting address to the UN Security Council, US Ambassador Nikki Haley said Tuesday's ICBM test had made "the world a more dangerous place," and that Washington was ready to use force if need be to deal with the threat of a nuclear-armed Pyongyang.
The North's leader Kim Jong-Un described the ICBM launch -- staged on the US Independence Day holiday -- as a gift to "American b******" and vowed to give more "gift packages" to the US in the future.
The impoverished North is already under onerous international sanctions imposed over its past nuclear and missile tests held in violation of UN resolutions, which ban it from using any ballistic or nuclear technologies.