"If Park does not accept the Constitutional Court's decision, it would be an insult against the people and the Constitution," Moon told reporters after a ceremony to launch the job creation panel on his campaign team.

"It is the final duty of Park to lend a hand in overcoming conflict and (healing) the wounds of the people by delivering an apology and accepting the result," the potential candidate added.

Moon also reaffirmed his recent remark that South Korea should be prepared for disparities in policy with the United States.

Although the United States is a close ally, Seoul should say "no" whenever necessary to protect national interests, he said.

"Seoul and Washington are extremely important allies. But in the face of the harsh international environment, the ally's interest does not necessary match ours. Although we can come together for the big picture, we should also know how to secure national interests with confidence," Moon added.

In line with the stance, Moon said South Korea will prioritize its national interests when discussing the free trade agreement and the sharing of defense costs with Washington.

US President Donald Trump has been insisting that the two countries renegotiate the terms of the trade and military agreements, citing US national interests. (Yonhap)