Washington, Aug 9 (IANS): North Korea has successfully produced a miniaturized nuclear warhead that can fit inside its missiles, the Washington Post reported on Tuesday.

The conclusion was made in a confidential assessment completed last month by the Defense Intelligence Agency, the newspaper said, citing anonymous US intelligence officials.

"The IC (intelligence community) assesses North Korea has produced nuclear weapons for ballistic missile delivery, to include delivery by ICBM (intercontinental ballistic missile)-class missiles," the assessment states, in an excerpt read to The Post.

The assessment's broad conclusions were verified by two US officials familiar with the document, said the Post, adding that the development signals that North Korea has crossed "a key threshold on the path to becoming a full-fledged nuclear power".

The Japanese Defense Ministry has also warned that the threat posed by Pyongyang nuclear weapons programme has entered "a new stage".

"It is possible that North Korea has already achieved the miniaturization of nuclear weapons and has acquired nuclear warheads," the ministry said in a report released on Tuesday, according to NBC news.

On Saturday, United Nations Security Council unanimously adopted a US-drafted resolution that aims to slash by a third the North Korea's $3 billion annual export revenue over Pyongyang's two ICBM tests in July.

The resolution would ban Pyongyang's exports of coal, iron, iron ore, lead, lead ore and seafood. It would also prohibit countries from increasing the current numbers of North Korea's laborers working abroad, ban new joint ventures with Pyongyang and any new investment in current joint ventures.