A new U.S. military intelligence assessment says for the first time that North Korea may have developed a nuclear device small enough to mount on a ballistic missile, but said such a weapon's "reliability would be low."

In an assessment by the Defense Intelligence Agency, a branch of the Pentagon, analysts appeared to upgrade U.S. estimates of North Korea's nuclear-weapons abilities, according to a portion of the report disclosed by a lawmaker at a House hearing on Thursday.

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