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SEOUL — North Korea declared Sunday that it could test-launch an intercontinental ballistic missile, or ICBM, at any time from any location set by leader Kim Jong Un, saying a hostile U.S. policy was to blame for its arms development.

Kim said Jan. 1 that his country was close to test-launching an ICBM.

"The U.S. is wholly to blame for pushing [North Korea] to have developed an ICBM as it has desperately resorted to anachronistic policy hostile toward [North Korea] for decades to encroach upon its sovereignty and vital rights," an unnamed Foreign Ministry spokesman was quoted as saying by the official KCNA news agency.

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"Anyone who wants to deal with [North Korea] would be well advised to secure a new way of thinking after having clear understanding of it," the spokesman said.

Defense Secretary Ash Carter said Sunday that North Korea's nuclear weapons capabilities and ballistic missile defense programs constituted a "serious threat" to the United States and that it was prepared to shoot down a North Korean missile launch or test.

"We only would shoot them down ... if it was threatening, that is, if it were coming toward our territory or the territory of our friends and allies," Carter said on NBC's "Meet the Press."

The United States said Thursday that North Korea had demonstrated a "qualitative" improvement in its nuclear and missile capabilities after an unprecedented level of tests last year.

North Korea has been testing rocket engines and heat shields for an ICBM while developing the technology to guide a missile after re-entry into the atmosphere following liftoff, experts have said.

While Pyongyang is close to a test, it is likely to take some years to perfect the weapon, according to the experts.

Once fully developed, a North Korean ICBM could threaten the continental United States, about 5,500 miles away. ICBMs have a minimum range of about 3,400 miles, but some are designed to travel 6,200 miles or farther.

South Korean Unification Ministry spokesman Jeong Joon-hee said there were no signs of any launch preparations. But Defense Ministry spokesman Moon Sang-gyun called North Korea's statement a "provocative announcement" and said at a regular news briefing that Pyongyang would face stronger sanctions if it were to launch an ICBM.

Asked for comment Sunday, the White House referred to comments last week in which White House press secretary Josh Earnest said the U.S. military believed it could protect against the threat emanating from North Korea.

North Korea has been under U.N. sanctions since 2006 over its nuclear and ballistic missile tests. The sanctions were tightened last month after Pyongyang conducted its fifth and largest nuclear test on Sept. 9.