North Korea has demanded South Korea apologise for "despicable conservative riff-raff" prostesters who burned an image of Kim Jong-un in Seoul.
The incident threatened to undermine an agreement that athletes from North Korea would attend February’s Pyeongchang Winter Olympics in South Korea.
Organisers have sought to promote the event as a "Peace Olympics" to open a door for dialogue.
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But a group of right-wing activists set the image of Mr Kim on fire at a rally in Seoul on Monday, along with the North’s national flag, prompting a denunciation by Pyongyang.
It came as Pyongyang officials ended a rare trip to the South to prepare for planned concerts by the North’s artistic troupes during the Games.
The trip, led by the leader of the North’s popular Moranbong girl band, was the first time Pyongyang officials had visited the South for four years.
In a statement, the North’s Committee for the Peaceful Reunification of the Country called the protesters in Seoul "human rejects devoid of appearance as human beings" and added: "They are a despicable group of gangsters in human form."
The statement, released by the state-run KCNA news agency, accused them of committing "a never-to-be-condoned hideous crime" and said they were the "dregs of history" and "conservative riff-raffs".
It said Seoul should "throw overboard the rubbish so that they would not give off a stinking smell anymore" and "apologise before the nation".
The protests were a deliberate attempt turn the Olympics into a "theatre for escalating confrontation,” North Korea claimed.
If North Korea’s participation in the Games was cancelled the blame would rest "wholly with the South Korean authorities," the statement said.
In response to the protests and controversy South Korea’s presidential office called on the public to welcome all countries participating in the Games.
Presidential spokesman Park Soo-Hyun said: "The people have to all work together. Let us welcome the guests as dignified hosts."