U.S. officials have told CNN that North Korea is ready to conduct another nuclear test any time.

On Friday, the broadcaster quoted two unnamed U.S. officials as saying that specific intelligence indicators show the North is ready for its sixth underground nuclear test at any time.

The officials said recent satellite imagery indicates a "potentially significant change" at the Punggye-ri test site. They said satellites had observed for weeks "extensive activity on the surface," including vehicles, personnel and equipment as well as two tunnel entrances being dug out.

The most recent imagery shows activity has now stopped, and the officials noted that is a similar change in the pattern of activity just before previous tests. They said the signals indicate all final preparations are now complete.

Previously, Fox News cited a Pentagon official as saying the nuclear test could come as early as the end of the month. 

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