North Korea's communist regime has warned of a nuclear war on the Korean peninsula while vowing to step up its atomic bomb-making programme in defiance of new UN sanctions.
The north's defiance presents a growing diplomatic headache for US president Barack Obama as he prepares for talks on Tuesday with his South Korean counterpart.
South Korean president Lee Myung-bak told security-related ministers to "resolutely and squarely" cope with the morth's latest threat.
A commentary in the north's main state-run Rodong Sinmun newspaper, carried by the official Korean Central News Agency, claimed the US has 1,000 nuclear weapons in South Korea.
North Korea "is completely within the range of US nuclear attack and the Korean peninsula is becoming an area where the chances of a nuclear war are the highest in the world", the Tongil Sinbo commentary said.
Kim Yong-kyu, a spokesman at the US military command in Seoul, called the latest accusation "baseless", saying Washington has no nuclear bombs in South Korea. US tactical nuclear weapons were removed from South Korea in 1991 as part of arms reductions following the Cold War.
South Korea's unification ministry issued a statement demanding the North stop stoking tension, abandon its nuclear weapons and return to dialogue with the south.
North Korea's foreign ministry threatened war on any country that dared to stop its ships on the high seas under the new sanctions approved by the UN Security Council on Friday as punishment for the North's latest nuclear test.
