SEOUL, South Korea — Just days after North and South Korea agreed to hold their first high-level government meeting in six years, the plans appear to have collapsed over a disagreement about whether the intended delegations were of similar rank.

South Korea said that the talks, scheduled to start on Wednesday, were canceled but that it was still open to dialogue with the North.

The agreement to meet had been seen as a clear sign that the two Koreas were moving toward a thaw after years of recriminations. The tensions reached a peak this year when the North’s third nuclear test prompted broad international sanctions and the North responded with threats that it could launch nuclear strikes against South Korea and the United States.

But right up until the eve of the talks, North and South Korea were arguing over who should be their chief delegates to the meeting.