Amid continued threats from North Korean leader Kim Jong Un, the United States' expensive, ground-based interceptors "can't yet be counted on to shoot down a nuclear-armed missile," the Pentagon's weapons testing office has concluded in its annual report. That means that should North Korea launch an attack, the defense system has just a "limited capability to defend the U.S. homeland from small numbers of simple" intercontinental ballistic missiles (ICBMs), Bloomberg reported Tuesday, after obtaining an advance copy of the testing office's report.

North Korea has continued its nuclear tests in recent months, while Kim has claimed that the country is in the final stages of developing reliable ICBMs that could carry a nuclear warhead. But because of a lack of testing and simulations, the U.S. cannot accurately predict the likelihood it could stop a missile attack, the Pentagon report concludes.

U.S. leaders, however, have said otherwise in public remarks. Defense Secretary Ash Carter said Sunday on NBC News' "Meet the Press" that the U.S. can and would stop a nuclear attack from North Korea.

"If it were threatening to us, yes," he said. "That is, if it's predicted impact or one of our friends or allies, yes, we would shoot it down."

And Vice Admiral James Syring, the director of the missile defense agency, told Bloomberg he has "high confidence" in the defense system.

"I am very confident in the systems and procedures [the U.S. Northern Command] will employ to intercept a North Korean ICBM were they to shoot it toward our territory," he said to Bloomberg.

President-elect Donald Trump, meanwhile, recently posted to Twitter, "it won't happen," regarding North Korea developing a nuclear weapon that could reach the U.S.

Kim had threatened for months to attack U.S. and its ally, South Korea, by any means. 

"Research and development of the cutting-edge tech weapons are actively progressing and strengthening our defense capabilities, including last stage preparation of tests for Intercontinental Ballistic rocket launch have been continuously succeeding," Kim said in his New Year's remarks.