White House Chief of Staff and former Marine Gen. John Kelly told reporters that Americans ought to be concerned about nuclear developments in North Korea, as they directly impact their safety and U.S. national security.

Kelly, who said the North was working hard to develop an intercontinental ballistic missile capable of hitting all or parts of the U.S., noted cryptically if the threat grows “beyond where it is today, well, let’s hope that diplomacy works.”

He said that Pyongyang “is developing a pretty good nuclear re-entry vehicle,” which is necessary for a missile to strike its intended target; reentry vehicles must be able to withstand the heat of re-entering the Earth’s atmosphere without breaking up.

The former Marine leader’s comments seem to suggest that North Korea is close to developing this capability.

Kelly also told reporters that North Korea is a pariah state that cannot be permitted to threaten the U.S. or its allies.

“The American people should be concerned about a state that has developed a pretty good ICBM capability and is developing a pretty good nuclear re-entry vehicle,” Kelly said in his first White House press briefing since joining the administration earlier this year. “I would believe, I think I speak for the administration, that that state simply cannot have the ability to reach the homeland.”

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