North Korea could develop weapons within the next two years that may be capable of reaching and striking Britain, MPs have heard.
Kim Jong Un's regime in recent months has conducted several increasingly sophisticated nuclear tests as it expanded its missile programme - prompting a rise in international tensions.
Defence minister Earl Howe told the cross-party Defence Committee that the capability of North Korea has been "significantly developed" over the past few years.
"We judge that they are capable of, certainly now, of reaching targets in the short range - by which I mean Japan, South Korea obviously and adjoining territories," he said on Tuesday.
"Our judgment is it is probably six to 18 months before they will have an Intercontinental Ballistic Missile capability capable of reaching the coast of the United States or indeed ourselves."
But he warned that it is important to highlight how it is not deemed to be the case that Mr Kim's "programme is directed at the UK", adding how the threat to Britain "is not significant".
Asked whether North Korea's nuclear capability of striking the UK in two years places an additional premium on maintaining Britain's nuclear deterrent, Earl Howe agreed it does.
"I think whenever we debate the issue of the UK deterrent, the North Korean weapons programme is cited as a prime example of why we can never be complacent," he added.
Foreign Office minister Mark Field told MPs North Korea's "illegal pursuit of nuclear weapons does inevitably pose a serious and growing threat to the international peace and security".
He told the committee there is "little doubt" that the timeline of six to 18 months has "drastically reduced" over the last year, but stressed that conflict is not inevitable.
Mr Field said the UN and international community are continuing to put a "huge amount of pressure" onto North Korea "through all the means that we can".
The Tory MP said there is a sense that Mr Kim "wants to come out of the shadow of his father and particularly his grandfather".
"Part of that is to assert himself - 'I am the person who has been able to put us onto the nuclear top table' - which is obviously where he would hope to be if he is able to get fully fledged nuclear weapons," he added.
Mr Field also said the message is "loud and clear" for any country going forward, that nuclear weapons are the "ultimate insurance policy" and provide an exemption from being threatened.
But Earl Howe stressed: "Kim Jong Un knows that any attack by North Korea on South Korea or anywhere else, or use of nuclear weapons in any context, would be met with an overwhelming response."
Pressed on whether the UK would support a limited strike by the United States, Mr Field said any "direct action would have to be within international law" and the UK's support would only be if it had been sanctioned in advance.
With many Britons based in the region, both permanently and temporarily, Mr Field confirmed to MPs that an evacuation plan is "under constant review".
Earlier this month, the American President suggested he has developed a "very good relationship" with the North Korean leader, despite engaging in a war of sharp words.
The pair have traded insults over the last year, as North Korea accelerated weapons tests and appears on the cusp of having a nuclear-tipped missile that could strike the US mainland.
President Trump has called Mr Kim "Rocket Man" on a "suicide mission", and the regime's dictator has said the 71-year-old American president is "the mentally deranged US dotard".
America has publicly blamed the country and said they were "directly responsible" for the WannaCry cyber attack which hit the NHS and networks around the world last year.
But Earl Howe said that the UK was probably not the intended target, which instead was, as he understands it, South Korea.
"I think that Kim probably didn't care very much who or what was affected," he added when asked if the UK was attacked by accident.
"The balance of probabilities is that the UK was probably not necessarily a target that was intended in the first instance."