Recent tests have shown surprising technical advances by the secretive country’s weapons scientists.

will have advanced from prototype to assembly line, according to officials familiar with the document. Already, an aggressive testing regime 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.

The DIA and the Office of the Director of National Intelligence declined to address any classified assessments. But Scott Bray, ODNI’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 “reentry” — 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 reentry 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 to discuss sensitive military assessments.

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 as 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