North Korea threatened a nuclear strike on "the heart of the US"  CNN July 25 2017
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North Korea said it will launch "thousands-fold" revenge against the U.S. CNBC Aug 7 2017
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"the U.S. mainland is on the crossroads of life and death." same article as above
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https://www.sulphurtimes.com/opinion/north-korea%E2%80%99s-threats

Etc.

So Kim's comments are largely intended for propaganda value.