By Jill Dougherty and Adam Levine

The sudden death of Kim Jong Il is the "biggest shock you could have thrown into Asia," an expert on North Korea told CNN late Sunday night.

Victor Cha, who worked in White House National Security Council, says one of the likelier scenarios under which the North Korean regime could crumble was the sudden death of Kim Jong Il - and now it has happened.

"No one has any idea of what comes next," Cha said. "We are in unknown territory."

That uncertainty should have people on edge, a U.S. official told CNN's Pam Benson.

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