South Korea has continued an escalating rhetorical battle on the Korean Peninsula, with an official saying rival North Korea "must disappear soon".
South Korean defence ministry spokesman Kim Min-seok also said that North Korea is not a real country and exists for the benefit of only one person, a reference to dictator Kim Jong Un.
He said the North has no human rights or public freedoms.
The comments followed a series of sexist and racist slurs by North Korea against the leaders of South Korea and the United States.
Pyongyang's state media likened South Korean president Park Geun-hye to an "old prostitute" and US president Barack Obama to a "monkey" in recent dispatches.
Pyongyang's rhetoric intensified after Mr Obama and Ms Park met in Seoul last month.
South Korea has been highly critical of North Korea's nuclear and missile programmes, including recent rocket and missile tests and apparent preparations for a fourth nuclear test.
But the comments from Seoul today are stronger than normal. South Korea tries to avoid publicly talking about anything that could be interpreted as a collapse of the North Korean government because of worries that Pyongyang would raise tensions.
Pyongyang has been ramping up its rhetoric against Seoul and Washington since Mr Obama and Ms Park met in Seoul last month.
During that visit, Mr Obama said that it may be time to consider further sanctions against North Korea and that the US will not hesitate to use its military might to defend its allies.
South Korea has called the North's verbal insults against Ms Park immoral and unacceptable. The US state department described the North's racist slurs against Mr Obama as "disgusting".
Worries about renewed tension on the Korean Peninsula have recently deepened with Pyongyang threatening to conduct its fourth nuclear test to protest against what it calls US and South Korean hostility.
North Korea's barrage of rocket and missile tests earlier this year drew condemnation from South Korea, the United States and others. The North says the tests were part of military training aimed at coping with annual Seoul-Washington springtime military drills that Pyongyang calls an invasion rehearsal.