The United States and South Korea should step up planning for potential instability in North Korea, a former senior U.S. diplomat and currently a key foreign policy adviser to Democratic presidential nominee Hillary Clinton has said.

"One of the most vital tasks for the United States and South Korea is to prepare for instability and uncertainty in North Korea through greater contingency planning and coordination. On this question of profound change occurring suddenly on the Korean Peninsula, there are only two options for the alliance: being ill prepared and being very ill prepared," former Assistant Secretary of State Kurt Campbell said in his recent book, "The Pivot."

"The United States and South Korea should always strive for the former through exercises planning, and frequent dialogue on the full range of possible North Korean provocations -- from artillery strikes to nuclear contingencies -- as well as on the various follow-on repercussions, which could include a North Korean collapse, massive refugee flows and Chinese military interventions," he said.

Campbell, who is credited as being a key architect of President Barack Obama's "pivot to Asia" policy, is considered one of the top foreign policy brains for Clinton, along with former Undersecretary of State Wendy Sherman and former White House official Jake Sullivan.

In May, Sherman also called for greater contingency planning on North Korea, saying the current status quo likely is not sustainable, and unexpected changes, including a sudden regime collapse or a coup in the communist nation, cannot be ruled out.

Campbell also voiced strong opposition to transferring the wartime operational control, known as OPCON, of South Korea forces from the U.S. to the South, saying the transfer could cause confusion in the middle of a crisis.

In 2014, Seoul and Washington postponed the OPCON transfer until the right conditions are created for the transfer.

"If war does break out on the Korean Peninsula, U.S. and South Korean forces will fall under the bilateral Combined Forces Command, which is led by a U.S. general and gives the United States wartime operational control of the South Korean military," Campbell said.

"Although some South Korean politicians have expressed a desire to dismantle CFC and transfer OPCON to the South Korean military, the status quo should be maintained," he said. "The prevailing argument has served both countries for decades and a transfer could reduce cooperation and create confusion in the midst of crisis." (Yonhap)