PYONGYANG (CNN) –North Korea has taken a major step forward in realizing its goal of becoming a nuclear power, according to a Washington Post report on a confidential US intelligence assessment that concludes Pyongyang has developed a nuclear warhead capable of fitting inside its missiles.

The Washington Post first reported details of the assessment on Tuesday just hours after North Korea threatened ‘physical action’ in response to punitive sanctions unanimously passed by the United Nations Security Council over the weekend in response to Pyongyang’s two intercontinental ballistic missile tests in July.

“The IC [intelligence community] assesses North Korea has produced nuclear weapons for ballistic missile delivery, to include delivery by ICBM-class missiles,” the assessment states, in an excerpt read to The Washington Post.

CNN has not independently verified the report.

The Washington Post story says that it is not known whether North Korea has successfully tested the smaller design.

CNN has previously reported that US intelligence estimates Pyongyang may have the capacity to deliver a nuclear weapon to the US mainland by early next year.

This story is breaking and will be updated.

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