The United States, South Korea and other regional powers should launch discussions about how to handle potential contingencies in the North, such as a regime collapse or a coup, former U.S. Under Secretary of State Wendy Sherman said Tuesday.

Sherman, considered a key foreign policy brain for Democratic presidential front-runner Hillary Clinton, made the remark during a discussion at the Center for Strategic and International Studies, stressing that China's preferred status quo on the Korean Peninsula is "not sustainable."

"There has been little discussion with China about how all of the parties will respond in the event of a sudden collapse of the regime or coup in Pyongyang, a military confrontation resulting from a necessary response to a North Korean attack, or some other scenario," Sherman said.

"It is becoming increasingly clear that the status quo likely is not sustainable, and unexpected changes, including sudden regime collapse or a coup, cannot be ruled out," she said. "Frank discussions between the United States and China, together with South Korea, and Japan could enable both sides to find more areas of agreement than have existed in the past."

Key issues that should be discussed include what near term actions would U.S., South Korean, and Chinese forces take in the event of a regime collapse, how could conflict on the peninsula between those forces be avoided and how to secure the North's nuclear weapons and materials, Sherman said.

Other issues include whether American troops stay on the peninsula, how the Korean peninsula would be governed, what would replace the armistice and who would cover the economic costs of reconstruction, she said.

"These are just a few of the topics that will need to be addressed in order to help build, over the longer-term, a better understanding of the emerging strategic thinking of all of the parties," Sherman said.

These conversations will not be easy, especially in the coming year as China focuses internally on its 19th Party Congress, but such discussions are "necessary, and could potentially help better inform all the parties as they undertake a comprehensive reassessment of their core strategic interests and next steps," she said.

She also called for "serious, tough diplomacy" to deal with the North.

"The threat of North Korea is one of the greatest security challenges facing the world today," she said. "The elements of a strategy include ratcheting up sanctions internationally, continuing military exercises, missile defense, focusing on human rights and developing a common understanding of what happens if there is a collapse." (Yonhap)