A new report from the Associated Press lists four reasons why North Korea looms over U.S. defense chief Jim Mattis’s upcoming Asia trip.

North Korea’s threat to test launch an intercontinental ballistic missile that could potentially reach U.S. territory is pushing the Trump administration to step up its policy formation on the North.

Additional nuclear tests by the North are listed as another factor demanding Washington's attention. Trump has suggested in the past South Korea and Japan may need to obtain nuclear weapons of their own.

The other two factors mentioned are North Korea's increasing capacity to produce weapons-grade plutonium and its belligerent reaction to annual joint South Korea-U.S. military exercises in March.

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