Leader Kim Jong Un presided over the launches, "feasting his eyes on the trails of ballistic rockets," the report from the Korean Central News Agency said, in language that will only heighten tensions in the region.
The four ballistic missiles fired Monday morning were launched by a military unit "tasked to strike the bases of the U.S. imperialist aggressor forces in Japan," the KCNA report said.
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The United States has numerous military bases in Japan, part of its post-war security alliance with the country.
Three of the four missiles flew about 600 miles over North Korea and landed in the sea, within Japan's exclusive economic zone off the Oga peninsula in Akita prefecture, home to a Japanese self-defense forces base. The fourth fell just outside the EEZ.
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Shinzo Abe, Japan's prime minister, said Monday that the launches "clearly show that North Korea now poses a new level of threat."
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The U.S. Strategic Command said its systems detected and tracked the projectile but "determined the missile launch from North Korea did not pose a threat to North America."
North Korea did not say what kind of missiles it had fired, but with a maximum height of 160 miles, analysts said they were probably medium-range Rodongs or extended-range Scuds.
Analysts are waiting on photos to be released by North Korean media to make further assessments.
The KCNA statement said that Kim supervised a rocket launching drill of the Hwasong artillery units, an elite missile division in the Korean People's Army's Strategic Force.
"Respected Supreme Leader Kim Jong Un learned in detail about the preparations for fire strike while going round the ballistic rocket launching grounds," the report said. "At an observation post he was briefed on a launching plan and gave an order to start the drill."
Kim noted that the four missiles, launched simultaneously, "are so accurate that they look like acrobatic flying corps in formation," according to the report.
The 33-year-old marshal also ordered the strategic forces to be on high alert "as required by the grim situation in which an actual war may break out anytime, and get fully ready to promptly move."
The launches coincided with joint U.S.-South Korean military exercises on the southern half of the Korean Peninsula, drills that take place every year and which North Korea views as preparation for an invasion.
Both Abe and South Korea's prime minister, Hwang Kyo-ahn, strongly condemned Monday's launches, while China's foreign ministry said it "opposes" them.
In New York, a spokesman for the U.N. Secretary-General António Guterres said he condemned the actions, which "violate Security Council resolutions and seriously undermine regional peace and stability."
In Washington, White House press secretary Sean Spicer said "the Trump administration is taking steps to enhance our ability to defend against North Korea's ballistic missiles."
"The launches are consistent with North Korea's long history of provocative behavior," he told a press briefing Monday. "The United States stands with our allies in the face of this very serious threat."
