A senior Cheong Wa Dae official says North Korea could be making a serious mistake if its planned closures of the border and communication lines are intended to isolate South Korea from taking part in Pyongyang's diplomacy with the United States.

The official on Thursday told reporters that Seoul and Washington will continue to cooperate closely even after U.S. President-elect Barack Obama takes office.

The presidential official also said that a possible North Korean strategy to bypass South Korea in its discussions with the U.S. is an outdated notion.

The official added that the door for dialogue is always open, expressing deep regret over the latest moves by the North.

In a message sent to Seoul Wednesday, the North Korean military threatened to thoroughly restrict all overland passage through the inter-Korean border from December first.