Mount Kumgang was meant to showcase co-operation
North Korea has threatened to take "extraordinary measures" unless South Korea lifts its ban on tours to Mount Kumgang resort, an official said.
The warning was issued to a group of South Korean businessmen, who visited the resort after Pyongyang threatened to seize their assets if they did not.
Built with South Korean money, the resort used to earn North Korea tens of millions of dollars a year.
But tours were suspended when a South Korean tourist was shot dead.
Housewife Park Wang-ja, 53, was killed by North Korean guards on 11 July 2008 on a beach near the resort.
South Korea says it wants the killing - when the tourist allegedly strayed into a military area - properly investigated before it allows tours to resume.
The meeting at Mount Kumgang followed threats by the North to begin seizing South Korean-owned property.
Pyongyang last week summoned the companies, saying it wanted to conduct a survey of their property and that those who failed to attend would have their assets seized.
Seoul has questioned Pyongyang's explanation of the July 2008 shooting
According to Yonhap news agency, the group were told at a 15-minute meeting at the resort that the survey - the purpose of which is not clear - would take until 31 March.
They were also told that if Seoul did not agree to restart cross-border tours within a week, unspecified "extraordinary measures" would be taken, one of the South Korean officials there told Yonhap news agency.
North Korea has previously said that unless the tours restart, it will consider cancelling all agreements and contracts, and seek a new business partner.
Observers suggest that the North is becoming increasingly desperate for sources of foreign cash as it labours under a strict sanctions regime, and still suffers the effects of last year's badly managed currency reform.
Mount Kumgang, which was meant to symbolise inter-Korean co-operation, looks increasingly like a token of continuing mistrust and tension, our correspondent says.