North Korea will be able to field a reliable, nuclear-capable intercontinental ballistic missile as early as next year, U.S. officials have concluded in a confidential assessment that dramatically shrinks the timeline for when Pyongyang could strike North American cities with atomic weapons.

The new assessment by the Pentagon’s Defense Intelligence Agency (DIA), which shaves a full two years off the consensus forecast for North Korea’s ICBM program, was prompted by recent missile tests showing surprising technical advances by the country’s weapons scientists, at a pace beyond which many analysts believed was possible for the isolated communist regime.

The U.S. projection closely mirrors revised predictions by South Korean intelligence officials, who also have watched with growing alarm as North Korea has appeared to master key technologies needed to loft a warhead toward targets thousands of miles away.

The finding further increases the pressure on U.S. and Asian leaders to halt North Korea’s progress before it can threaten the world with nuclear-tipped missiles. President Donald Trump, during his visit to Poland earlier this month, vowed to confront Pyongyang “very strongly” to stop its missile advances.

The DIA has concluded that North Korean leader Kim Jong Un will be able to produce a “reliable, nuclear-capable ICBM” program sometime in 2018, meaning that by next year the program will have advanced from prototype to assembly line, according to officials familiar with the document. Already, the aggressive testing put in place in recent months has allowed North Korea to validate its basic designs, putting it within a few months of starting industrial production, the officials said.

Working on re-entry missile

But Scott Bray, U.S. national intelligence manager for East Asia, said in a statement: “North Korea’s recent test of an intercontinental range ballistic missile — which was not a surprise to the intelligence community — is one of the milestones that we have expected would help refine our timeline and judgments on the threats that Kim Jong Un poses to the continental United States. This test, and its impact on our assessments, highlight the threat that North Korea’s nuclear and ballistic missile programs pose to the United States, to our allies in the region, and to the whole world. The intelligence community is closely monitoring the expanding threat from North Korea.”

One of the few remaining technical hurdles is the challenge of atmospheric “re-entry” — the ability to design a missile that can pass through the upper atmosphere without damage to the warhead. Long regarded as a formidable technological barrier for impoverished North Korea, that milestone could be reached beginning with new tests expected to take place within days, U.S. analysts said. U.S. officials have detected signs that North Korea is making final preparations for testing a new re-entry vehicle, perhaps as early as Thursday, a North Korean national holiday marking the end of the Korean War.

“They’re on track to do that, essentially this week,” said a U.S. official familiar with the intelligence report who, like others, insisted on anonymity.

North Korea has not yet demonstrated an ability to build a miniaturized nuclear warhead that could be carried by one of its missiles. Officials there last year displayed a sphere-shaped device the regime described as a miniaturized warhead, but there has been no public confirmation that this milestone has been achieved. Preparations reportedly have been underway for several months for what would be the country’s sixth underground atomic test. The last one, in September, had an estimated yield of 20 to 30 kilotons, more than double the explosive force of any previous test.

‘Alarming progress’

North Korea startled the world with its successful July 4 test of a missile capable of striking parts of Alaska — the first such missile with proven intercontinental range. The launch of a two-stage “Hwasong-14” missile was the latest in a series of tests in recent months that have revealed startlingly rapid advances across a number of technical fields, from mastery of solid-fuel technology to the launch of the first submarine-based missile, current and former intelligence officials and weapons experts said.

“There has been alarming progress,” said Joseph DeTrani, the former mission manager for North Korea for the Office of the Director of National Intelligence and a former special envoy for negotiations with Pyongyang. “In the last year they have gained capabilities that they didn’t have, including ones that we thought they would not have been able to obtain for years.”

The July 4 missile test also caught South Korea’s intelligence service off guard, prompting a hasty revision of forecasts, according to South Korean lawmakers who have received closed-door ­briefings.