The head of the North Korean working-level delegation, Park Yong-il (left) shakes hands with his South Korean counterpart, Lee Duk-haeng, during their talks at Tongilgak. Picture: Unification Ministry, Yonhap

Seoul - Barely a day after the two Koreas agreed to resume reunions for divided families, North Korea threatened on Thursday to renege on the deal unless the South scraps looming military drills with the United States.

“It's outrageous that (South Korea) is pushing ahead with aggressive war moves at a time when both sides reached a crucial agreement to realise national reconciliation and co-operation,” the North's top military body, the National Defence Commission (NDC), said.

In a rare example of cross-border co-operation, officials from North and South Korea agreed on Wednesday to hold a reunion on February 15-20 for several hundred relatives separated by the 1950-53 Korean conflict.

It would be the first such event in more than three years, and the accord was hailed as a possible harbinger of warmer ties between the arch rivals.

But Thursday's NDC statement appeared to back up those who had warned that Pyongyang would use the reunion agreement as a bargaining chip to extract concessions from Seoul.

South Korea and the United States are set to start a series of annual military exercises at the end of the month, and the North has repeatedly demanded that they be called off.

As well as the joint drills, the NDC also condemned “slanderous” attacks in the South Korean media, and indicated particular annoyance with reports of North Korean leader Kim Jong-un's recent visit to an orphanage.

A picture of Kim wearing shoes while interacting with the orphans in their dormitory was pilloried in the South. The leading conservative South Korean daily, the Chosun Ilbo, said it displayed an “unimaginable” lack of manners.

Koreans never wear outdoor shoes inside the home - especially in living areas.

“We cannot but reconsider the implementation of an agreement that was already reached as long as there is a continued move to hurt the dignity of our supreme leadership and slander our system,” the NDC statement said.