North Korea has postponed talks scheduled with the US-led United Nations Command about the sinking of a South Korean warship in March.
Pyongyang cited administrative reasons for the delay, UN officials said.
The sinking of the Cheonan killed 46 people and raised tensions sharply between the North and South Korea.
The meeting was due to take place on Tuesday in the truce village of Panmunjom. Its aim was to pave the way for future higher-level discussions.
The UN Command - which oversees the armistice that ended the Korean War - said the North had not proposed a new time for the talks.
North Korea has flatly denied accusations that it torpedoed the warship.
Pyongyang has also complained about forthcoming naval exercises by the US and South Korea, whose location has not yet been confirmed.
The drill, which analysts say is a show of strength in light of the alleged attack, comes despite strong protest from China.
Seoul is considering moving the location to its south or east coasts rather than the sensitive Yellow Sea, Yonhap news agency quoted a government source as saying.
The Cheonan went down on 26 March. International investigators say it was sunk by a North Korean torpedo.
Pyongyang denies responsibility for the incident, which happened near the disputed inter-Korean maritime border.
Following the sinking, North Korea suspended all contact with its southern neighbour, in response to Seoul's trade suspension.
A statement from the UN Security Council, released on Friday, praised South Korean "restraint" over the incident.
But it did not explicitly condemn North Korea - in a move correspondents say was a means of securing Chinese support for the statement.