Britain's secretary of defense, Michael Fallon, spoke on the BBC's primary Sunday morning show about Hurricane Irma, ZAPAD 17, Brexit, and North Korea. But Fallon's most revealing — and concerning — comment came when host Andrew Marr asked him about North Korea's intercontinental ballistic missile capabilities: "Do you believe that North Korea has a ballistic missile capable of hitting London?"

Fallon responded, "Not yet, but they are clearly accelerating their missile program, the range is getting longer and longer."

The declarative nature of that statement: "not yet" and "longer and longer," its framing (short and precise phrasing), and source (the defense secretary), mean Fallon's comments offer a window into U.S. intelligence assessments. Because the U.K. has limited intelligence collection on North Korea (aside from human intelligence opportunities at its Pyongyang Embassy), we can be confident that Fallon's comments represent U.S. assessments rather than British. Deep U.S.-U.K. intelligence sharing means that Fallon would be given U.S. material.

This means that Fallon would seem to be the first U.S. or British Cabinet official to confirm the Washington Post's July reporting that the U.S. intelligence community believes North Korea will attain a reliable nuclear warhead-ICBM capability in 2018.

Still, Fallon's qualification that North Korea has "not yet" reached an ICBM capability is relevant for two further reasons.

First, it forces us to ask what is delaying North Korea's reliable capability?

From my perspective, seeing North Korea can already fire high altitude distance intermediate range missiles with confidence, its outstanding challenge would seem to be fitting a warhead payload onto an ICBM that can travel thousands more miles. The complication here is that a warhead adds weight and thus fuel and trajectory complications to a successful launch, and from North Korea it's 4,500 miles to Honolulu, 5,000 to Seattle, or 5,400 miles to London.

Second, in noting the "accelerating" North Korean capability, Fallon corroborates the urgency that defines Trump's strategy on North Korea. With each new test, Kim Jong Un advances his progress towards ICBM feasibility. It is for that reason, as I noted last week, that the U.S. should now shoot down North Korean ICBMs*.

Regardless, we now have a window (albeit via a British official) as to why the Trump administration is so concerned about North Korea's ballistic missile program. They know that time remains to stop this program, but that time is rapidly running out.

* ... And help Kim find some new friends.