Small-scale exercises with South Korea have kept U.S. troops ready for conflict with North Korea, defense officials say.
Kim has used the diplomatic stalemate to expand his military capabilities by intensifying tests of shorter-range weapons.
Kim Jong Un called for his military to prepare unspecified “offensive measures” to protect the country’s security.
The action followed reports that North Korea had warned of a possible missile launch or nuclear test for late December.
Mount Paektu and white horses are symbols associated with the Kim family's dynastic rule.
It is the latest sign of impatience from Kim amid worries that two years of U.S.-North Korean diplomacy will fall apart.
North Korea responded to a tweet by President Trump that hinted at another summit with North Korean leader Kim Jong Un.
A North Korean official said there has been no substantial progress in relations despite warm ties between the two leaders.
Nuclear negotiations have been at a standstill following a February summit between Kim Jong Un and President Donald Trump.
North Korea said Friday it wants President Donald Trump to make a "wise option and bold decision."