Such changes of plans are largely attributable to diplomatic factors, sources familiar with the matter said.

As Seoul and Pyongyang have agreed to hold a state summit in April, any other non-governmental exchanges are granted lower priority under the current diplomatic climate, they said.

"The governments (of both sides) are concentrating all efforts on the 'big day' and it appears that they are brushing everything else aside," an official said, asking not to be named. "I bet Pyongyang is thinking the same."

A South Korean government official said any private exchange is always under consideration and will "be approved if they meet requirements," including following procedures and submitting necessary documents, such as an official invitation from the North.

Another obstacle for private-level exchanges is the tougher sanctions imposed by the United Nations Security Council and the ones imposed solely by the United States, sources said.

North Korea ratcheted up its nuke and missile offensives last year including its sixth and most powerful nuclear test. The UN and Washington have since imposed fresh sanctions against the communist regime, largely aimed at restricting shipments of oil and other goods.

"We need to check everything if they in any way violate the sanctions put forward by the UN and US, even if we reach an aid deal with the North," the official added. (Yonhap)