John Kerry is heading to the Korean peninsula to present a diplomatic front after threats from North Korea. David Gregory, moderator of "Meet the Press," said uncertainly over who leader Kim Jong-un is complicates the situation. TODAY's Lester Holt interviews David Gregory.

A senior defense official confirms that the Pentagon has delayed an intercontinental ballistic missile test that was scheduled for next week. The official says Secretary of Defense Chuck Hagel decided to postpone the test because of ongoing tensions with North Korea.

The test was "long planned and was never associated with North Korea to begin with," the official said, but added that "given recent tensions on the Korean Peninsula, it's prudent and wise to take steps that avoid any misperception or chance of manipulation, so the test has been postponed."

The test was planned for next week at Vandenberg Air Force Base in California. It would have tested the Minuteman 3 ICBM missile.

The U.S. will conduct another test soon, the senior defense official said, adding that the U.S. "remains strongly committed to our nuclear deterrence capabilities."

The unusual move follows recent warlike rhetoric from North Korea, which included a threat to attack U.S. bases in the Pacific.

North Korean authorities also told diplomatic missions they could not guarantee their safety starting next Wednesday -- after declaring that conflict was inevitable. There were also reports that North Korea had moved two medium-range missiles to a location on its east coast.

Reuters contributed to this report.