North Korea has threatened the South with "unspeakable disaster" if Seoul backs Washington's hardline approach to the nuclear crisis.
North Korea frequently issues aggressive rhetoric
The comments were made by the chief North Korean delegate at inter-Korean economic talks which opened in Pyongyang on Tuesday, and were publicised by the North's KCNA news agency.
They are the first official response to last week's summit between South Korean President Roh Moo-hyun and US President George W Bush in Washington last week, which saw an apparent hardening of South Korean policy towards the North.
Seoul and Washington threatened at the Washington meeting to take "further steps" against Pyongyang, if it continued to escalate tensions on the peninsula.
It was not clear what those "further steps" were, but they could include the adoption of sanctions, or even military action.
"The South side will sustain an unspeakable disaster if it turns to confrontation," Pak Chang-ryon, North Korea's chief negotiator at the inter-Korean economic talks warned on Tuesday.
"Should the South take the path of confrontation, talking about the so-called nuclear issue or 'further steps'... North-South ties would come to naught," he said.
North Korea's relations with the South and the US have been at boiling point since last October, when Washington said Pyongyang had admitted to a secret nuclear weapons programme.
Ms Calmy-Rey: The first foreign minister to walk over the border
The reaction from the North on Tuesday cast a cloud over the visit by the Swiss Foreign Minister, Micheline Calmy-Rey, who became the first foreign government minister to travel from North to South Korea by foot when she stepped across the border at the truce village of Panmunjom.
"It is a small step, but I hope it would be a great step towards peace here on the peninsula of Korea," she told reporters at the world's most heavily fortified border crossing.
The minister, who held four days of talks in Pyongyang, said Switzerland was willing to play a role as facilitator to try to resolve the crisis over North Korea's nuclear ambitions.
Switzerland has had formal diplomatic ties with North Korea for nearly 30 years, but this was the first time a government minister had made an official visit to the North.