The Pentagon has deployed high-tech radar to keep watch for a potential North Korean long-range-missile launch in the coming months, according to a US defense official.
It is the first US military response to Pyongyang's claim it could launch an intercontinental ballistic missile.
The sea-based X-band radar (SB-X) is able to track the long-range launches and provide crucial data.
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The radar, whose home port is in Hawaii, has deployed several times in the past to monitor North Korean missile activity. But it can only remain at sea for a certain, undisclosed, period of time, so military officials try to calculate the most significant times, the official said.
Generally the SB-X is sent north of Hawaii and stationed about halfway to Alaska for the optimum spot to track a potential North Korean missile launch headed for Alaska, Guam or the West Coast of the United States.
Additional surveillance assets are being identified to monitor activity on the Korean Peninsula, but the official declined to discuss any details.
Defense officials are emphasizing that if North Korea were to launch an intercontinental ballistic missile, it might not be shot down by a US missile defense system.
"If the missile's threatening, it will be intercepted. If it's not threatening, we won't necessarily do so," Defense Secretary Ash Carter told reporters Tuesday. "It may be more to our advantage to, first of all, save our interceptor inventory, and, second, to gather intelligence from the flight rather than do that (shoot it down) when it's not threatening."
The SB-X radar will increase the US ability to collect that type of missile data.
North Korean leader Kim Jong Un recently said the test launch of an ICBM is in its final stages.
US officials continue to say they do not believe the North Koreans have mastered the technology needed for the missile to re-enter the atmosphere.
There have been launches of three-stage long-range rockets with a satellite on the front end being boosted into space. The two technologies are very similar, but it is re-entry of the warhead that has not yet been demonstrated, US officials said.
On Wednesday, the US Treasury froze all US property interests and assets belonging to seven North Korean government officials. According to a statement, the Treasury imposed the sanctions because North Korea continues to engage in grave human rights abuses and actively uses censorship policies to conceal those abuses.
Most of the seven sanctioned North Koreans on the blacklist work in top-level security and prison operations. They include Kim's younger sister, Kim Yo Jong -- Vice Director of the Korean Workers' Party Propaganda and Agitation Department.
The Treasury further sanctioned the State Planning Commission and the Ministry of Labor, slamming the two government bodies for coordinating forced labor -- including in North Korean mines.
This is the second time the US has imposed human rights sanctions on Kim's government, after blacklisting Kim and other top officials in July.