A short-range missile test or rocket engine test by North Korea could come at any time, but a long-range intercontinental ballistic missile (ICBM) test – although possible – is not expected until after the first of the year, according to U.S. intelligence officials. Some of the websites that track the North using commercial satellite photos have noted activity at the Sohae launch facility, which has been used in the past to launch satellites, but so far U.S. intelligence is not seeing any preparations for a launch and says the activity could just be related to the winter training cycle.

It's traditional for North Korean leader Kim Jong Un to deliver a New Year's address, during which he generally lays out the strategic focus for the year and any major shifts in policy or engagement. North Korea experts are likely to be watching to see whether Kim uses the address to declare the diplomatic window with the U.S. is now closed and then take action by launching an ICBM. Or he could launch one between now and then and use the speech to explain why the test was carried out.

Kim has set a deadline for the end of the year for the U.S. to offer terms for a nuclear deal, and said this month that it's up to the U.S. to choose which "Christmas gift" it receives from the North.

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In February, negotiations stalled after a summit between Kim and Mr. Trump ended suddenly when the U.S. rejected North Korea's demand that the U.S. lift all sanctions in exchange for the opening by the North of one key nuclear facility to some inspection.

North Korea has been claiming recently that it has performed "crucial" and "very important" tests, possibly of missile-related technologies, announcing the completion of one such test as U.S. special representative for North Korea, Steve Biegun, just confirmed as deputy secretary of state, was traveling to South Korea in mid-December for nuclear discussions.

A short-range test would not be viewed as much of a provocation, given that Pyongyang has launched several in the past year and President Trump has largely ignored them. These tests do matter to South Korea and Japan (and our troops there) because short-range missiles have both countries in range.

In May 2018, North Korea made a big show of "demolishing" its main nuclear test site, inviting members of the press to view it. However, there hasn't been much evidence of major activity there since. That said, it has been suspected that the regime has an alternate site and that Punggye-ri (the site it says it blew up) was largely unusable because of the numbers of tests conducted there.

The Associated Press contributed to this report.