North Korea's leader Kim Jong Un has been briefed on his military's plans to launch missiles in waters near Guam.
It comes days after the Korean People's Army announced it is preparing to create "enveloping fire" near the US military hub in the Pacific.
During an inspection of the army's strategic forces, Mr Kim praised the military for drawing up a "close and careful plan".
He said he would watch the "foolish and stupid conduct of the Yankees" a little more before deciding whether to give the order for the missile test, the Korean Central News Agency said.
Mr Kim said North Korea will conduct the planned missile launches if the "Yankees persist in their extremely dangerous reckless actions on the Korean Peninsula and its vicinity" and that the US should "think reasonably and judge property" to avoid shame, the news agency said.
The Korean People's Army's strategic forces said last week it would finalise by mid-August a plan to fire four intermediate ballistic missiles near Guam, which is about 2,000 miles from Pyongyang, and send it to Mr Kim for his approval.
The North Korean report came after US defence secretary Jim Mattis said the US would take out any North Korean missile seen to be heading for American soil, and declared any such North Korean attack could lead to war.
Marine Corps General Joseph Dunford, the chairman of the Joint Chiefs of Staff, also said during a visit to South Korea on Monday that the US wants to peacefully resolve the deepening stand-off with North Korea.
But it is also ready to use the "full range" of its military capabilities in case of provocation, he said.