North Korea has threatened to cancel a reunion for families separated by the Korean War.
It comes "reckless" remarks by South Korean President Park Geun-Hye on Pyongyang's nuclear weapons program and human rights record.
Scrapping the October 20-26 event would effectively tear up an agreement the two Koreas reached in August to de-escalate tensions that had pushed them to the brink of armed conflict.
Addressing the UN General Assembly in New York on Monday, Park said the North's pursuit of a nuclear deterrent constituted a global threat and she urged the international community to join in pushing Pyongyang down a different path.
She also called on Pyongyang to improve its human rights record in the wake of a report by a UN Commission of Inquiry which concluded that North Korea was committing rights violations "without parallel in the contemporary world".
A statement issued late on Tuesday by a spokesman from the North's Committee for the Peaceful Reunification of Korea (CPRK) said Park's comments were "utterly bereft of reason" and proved she was "hell-bent" on confrontation.
"Due to the South Korean authorities' reckless confrontation row, not only North-South relations but the reunion of separated families ... has been put at serious peril," the spokesman said.
"The event may prove completely abortive," he added.
Millions of people were separated during the 1950-53 Korean conflict that sealed the division between the two Koreas.
Most died without having a chance to see or hear from their families on the other side of the border, across which all civilian communication is banned.
About 66,000 South Koreans - many of them in their 80s or 90s - are on the waiting list for an eventual reunion, but only a very limited number can be chosen each time.
Pyongyang has a lengthy track record of manipulating the divided families' issue for political purposes, refusing proposals for regular reunions and cancelling scheduled events over some perceived slight.
On Wednesday, the South's Unification Ministry said Pyongyang's threat to cancel was "very regrettable" and warned the North against seeking political "pretexts" for reneging on a humanitarian commitment.