|Experts say the ICBM launched by the North is capable of reaching major US cities|
If correct, it would be a considerable development in the rogue state's nuclear weapons programme - and a significant step on the path to becoming a fully fledged nuclear power.
According to the Washington Post, the claim is contained in a confidential assessment by America's Defence Intelligence Agency.
The paper quotes the assessment as saying: "The IC (intelligence community) assesses North Korea has produced nuclear weapons for ballistic missile delivery, to include delivery by ICBM-class missiles."
|North Korea launches intercontinental missile|
North Korea is believed to be working on extending the reach of its ICBMs to the US mainland by as soon as next year.
An analyst who specialises in North Korea, who asked not to be named, told Sky News: "This is possible. It's quite credible. It's not a surprise for anyone who knows North Korea considering what they did last year.
"They carried out six nuclear tests in the last decade and two in 2016. The last test was in September 2016."
He said it was impossible to say if any of the tests were of the miniaturised warhead, but said North Korea had stated it had produced a "standardised" warhead, which suggested it was a "compact" warhead.
In terms of where the country was in achieving its aims of producing a nuclear weapon that is capable of exploding above the US mainland, he said it was "a lot more than halfway".
Pyongyang has already shown it can produce a missile that is capable of hitting the US mainland, he added, but still has several more hurdles to overcome.
The analyst said North Korean scientists appeared to be yet to develop a targeting system to aim the missile accurately and a re-entry vehicle that would keep the warhead safe as it fell back to earth towards its target - two elements that fully-functioning nuclear ICBMs require.
But he added: "It's fair to say it's just a matter of time, in terms of being able to hit the hit the US with a (nuclear) missile."
Earlier, Pyongyang threatened to launch "thousands-fold" revenge against the US after tough UN sanctions were imposed on it following the test firing of ICBMs.
President Donald Trump tweeted: "After many years of failure, countries are coming together to finally address the dangers posed by North Korea. We must be tough & decisive!"
Two days ago, the UN Security Council
unanimously approved new sanctions to punish Pyongyang , including a ban on coal and other exports worth more than £770m.