North Korea and China Get Cozier on Trade: Expert

A layer of complexity underlying the saber-rattling in North Korea is Pyongyang's growing trade relationship with China, said John Park of Harvard University's Belfer Center for Science and International Affairs.

"It is increasing dramatically," Park told CNBC's "Squawk Box" on Thursday. "For North Korea, they might feel emboldened that they have capabilities and something that makes the South Koreans and U.S. in terms of offers for negotiations less attractive at this time."

On Wednesday, the U.S. said it would soon send a missile defense system to Guam following the North's repeated threats of a nuclear attack on American and South Korean interests. U.S. Defense Secretary Chuck Hagel called the situation a "real and clear danger."

Kim Jung-Un
Ed Jones | AFP | Getty Images
Kim Jung-Un

When it comes to the young new leader of North Korea, Kim Jong-un, son of deceased longtime ruler Kim Jong-il, there are "very little reference points," said Park.

"It's unclear if [Kim Jong-un] has gone through regime consolidation," he said. "So who is driving all of this is a big question mark."

North Korea had previously threatened a nuclear strike on the U.S. in the wake of new United Nations sanctions imposed on Pyongyang after it carried out its third nuclear test in February.

Last month, the North shutdown all of its official communication lines with South Korea, the U.S., and the U.N. That's particularly troubling, Park said, because "if there is an accident or escalation of some kind, there is no immediate emergency communication available."

North Korea has also barred entry to a joint industrial complex it shares with South Korea for a second day and threatened to close it.

Earlier in the week, Pyongyang said it was restarting the Yongbyon nuclear reactor to step up production of nuclear weapons materials.

By CNBC's Matthew J. Belvedere; Follow him on Twitter @Matt_SquawkCNBC. Reuters also contributed to this report.