Theresa May has called the latest North Korea nuclear weapons tests “reckless and unacceptable.”
The Prime Minister said in a statement: “This latest action by North Korea is reckless and poses an unacceptable further threat to the international community.
“I discussed the serious and grave threat these dangerous and illegal actions present with President Abe in Japan this week and reiterate the call we jointly made for tougher action, including increasing the pace of implementation of existing sanctions and looking urgently in the UN Security Council at new measures.”
“This is now even more pressing. The international community has universally condemned this test and must come together to continue to increase the pressure on North Korea’s leaders to stop their destabilising actions.”
The test came after propaganda pictures were published of Kim examining what was said to be a nuclear warhead being fitted on to the nose of an intercontinental ballistic missile.
United States President Donald Trump said on Twitter: “North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success. South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!”
Foreign Secretary Boris Johnson said: “There is no question that this is another provocation, it is reckless, what they are doing is they seem to be moving closer towards a hydrogen bomb which, if fitted to a successful missile, would unquestionably present a new order of threat.
“We have to consider how to respond and it’s our view in the UK, overwhelmingly, that peaceful diplomatic means are the best.”
Asked how close the crisis was to conflict, Mr Johnson said: “It’s certainly our view that none of the military options are good. It is of course right to say that all options are on the table, but we really don’t see an easy military solution.”
The proximity of South Korean capital Seoul meant the North “could basically vaporise” large parts of the country’s population even with conventional weapons, he warned.
The Chinese government “expressed firm opposition and strong condemnation” and urged North Korea to “stop taking erroneous actions that deteriorate the situation”.
But Mr Johnson urged Beijing to go further in putting economic pressure on its neighbour.
He said: “Our message to the Chinese is, and we are working ever more closely with them, we think there is more scope for you, the Chinese, to put economic pressure on the North Koreans.
“It has worked, we have seen signs in the last six months of Chinese pressure actually changing the approach of North Koreans – let’s see if we can do it again.”
The detonation was North Korea’s sixth and most powerful nuclear test to date.
The artificial earthquake triggered by the detonation was several times stronger than from previous blasts and reportedly shook buildings in China and Russia.
The test was carried out at 12.29pm local time at the Punggye-ri site where North Korea has conducted nearly all of its past nuclear tests.
Officials in Seoul put the magnitude of the quake at 5.7 while the US Geological Survey said it was a 6.3.