Economic talks between North and South Korea opened with a harsh warning from the North, and produced no progress on the crisis over Pyongyang's nuclear weapons programs.
North Korean delegates at the Pyongyang talks warned of "an unspeakable disaster" if Seoul turns to confrontation.
The comment in North Korean state media was Pyongyang's sharpest direct warning to the South in weeks, and its first public reaction to last week's meeting of the U.S. and South Korean presidents.
During that summit, South Korean President Roh Moo-hyun said inter-Korean exchanges would be linked to Pyongyang's moves to resolve the crisis over its nuclear weapons program. He agreed that "further steps" may be needed if the dispute worsens.
North Korean delegates call South Korea's cooperation with the United States "perfidious." But during the talks, they appealed to the South for 500,000 tons of food aid.
South Korea is ready to send grain to its impoverished neighbor, but wants monitors to verify that it goes to hungry civilians, not the military.
South Korean news reports say Seoul's delegates also warned Pyongyang that public opinion in the South would not support continued aid unless the nuclear issue is resolved. The economic talks end Thursday.
Delegates are expected to discuss transportation links, constructing a North Korean industrial complex, and establishing a joint tourism project.
But they may not make progress on those topics if the North continues to refuse to discuss the nuclear issue. North Korea insists the matter is strictly between it and the United States.
Pyongyang said it will end its nuclear program in exchange for a non-aggression pact and substantial economic aid from the United States.
The United States demands a verifiable end to North Korea's nuclear programs before it will discuss any other matters.
Washington said North Korea admitted in October it was secretly developing nuclear weapons, in violation of several international accords.
A few months later, North Korea pulled out of the Nuclear Nonproliferation Treaty and restarted a facility capable of producing weapons-grade plutonium. Just days ago, Pyongyang declared an inter-Korean agreement not to develop nuclear weapons was dead.