David Cameron has said the threat posed by North Korea is a "real concern" and underlined the need for the UK to maintain its nuclear deterrent.
The Prime Minister said the actions of Kim Jong Un's regime were "worrying and threatening" and the country had "extremely dangerous" weapons. He said maintaining the UK's nuclear capacity was a necessary "insurance policy against the risks that there are in the world".
Tensions on the Korean peninsula have heightened in recent weeks following a string of aggressive moves by the administration in Pyongyang. North Korea's military has warned that it has been authorised to attack the US using "smaller, lighter and diversified" nuclear weapons and reports suggest a missile with "considerable range" has been moved to the country's east coast.
The United States has announced that it will deploy a missile defence system to the US Pacific territory of Guam to strengthen regional protection against a possible attack.
Answering questions during a visit to Glasgow, Mr Cameron said he was "very concerned" about the situation.
North Korea has "extremely dangerous technologies in terms of nuclear and its weapons", he said. "It has a new and relatively unknown leader and obviously the noises it has been making in recent weeks and months are worrying and threatening."
He called for North Korea to abide by the United Nations resolution and ensure "that the heat is taken out" of the situation.
"It is a good moment to stand back and ask ourselves about the dangers there are in the world and the need to maintain strong defences," he said. "North Korea does now have missile technology that is able to reach, as they put it, the whole of the United States. If they are able to reach the whole of the United States they can reach Europe too, they can reach us too. That is a real concern."
The comments underline the Conservatives' commitment to a like-for-like replacement for the ageing Trident submarine fleet while their Liberal Democrat coalition partners are seeking a cheaper alternative.
Mr Cameron said: "The question we need to ask ourselves in the context of this debate about the nuclear deterrent is what will a country like North Korea be like in 10 years, 15 years, 20 years? How certain can we be? How certain can we be that its weapons will be secure? How certain can we be that they won't share weapons and technologies with other countries?"