The Missile Defense Agency said it was the first live-fire test against a simulated ICBM for the Ground-based Midcourse Defense (GMD), managed by Boeing Co (BA.N), and hailed it as an "incredible accomplishment".
But she cautioned that it was "one of several tests needed" to demonstrate that the system is capable of defending the US and said further analysis "is also needed to ensure that no further changes are needed to the interceptors now undergoing production".
The Security Council first imposed sanctions on Pyongyang in 2006 over its ballistic missile and nuclear programs and has ratcheted up the measures in response to five nuclear tests and two long-range missile launches.
Tuesday's test followed Pyongyang's launch of a suspected Scud missile Monday, which landed in the sea within Japan's exclusive economic zone.
While Tuesday's test wasn't designed with the expectation of an imminent North Korean missile threat, the military wants progress toward the stated goal of being able to shoot down a small number of ICBMs targeting the U.S. Then, in theory, the control centers in the U.S. can use that information to guide an interceptor missile to knock into the enemy weapon while it's still in space - away from people - and smash it into smithereens.
The Pentagon is still incorporating engineering upgrades to its missile interceptor.
The American interceptor has an uneven track record, having succeeded nine times out of 17 attempts against missiles in test since 1999, although the most recent test - in June 2014 - was a success.More news: White US policewoman cleared in black man's shooting death
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But "in a more broad sense", Davis said, "North Korea is obviously one of the reasons why we have this capability". The target is not a mock-up of an actual North Korean ICBM, and details of its exact capabilities have not been made public.
The Pentagon on Tuesday announced it had successfully conducted its first live-fire test against a simulated intercontinental ballistic missile capable of striking the USA mainland.
North said the move is seen as a preventative measure in the wake of North Korea's threats against the United States.
With news of North Korea continuing to test their long range missiles it appears that the U.S.is taking added precautions in the event that they succeed.
That test involves firing a new version of the military's single long-range ground-based interceptor missile, which is now based in Alaska and California.
"Overall", she wrote in an analysis prior to the test, the military "is not even close to demonstrating that the system works in a real-world setting".
The U.S. military fired an ICBM-type missile from the Kwajalein Atoll in the Marshall Islands toward the waters just south of Alaska.
In addition to the missile interceptors, however, the Pentagon said it has other more reliable options of defense, including the Terminal High-Altitude Area Defense, which was deployed to South Korea this year.