Donald Trump has claimed the threat from North Korea will be met with "fire and fury like the world has never seen" if they continue to expand their nuclear and missile programmes.

The comments come after reports that North Korea had produced a nuclear warhead small enough to fit on an intercontinental ballistic missile (ICBM).

In a press conference at his Bedminster, New Jersey property, Mr Trump warned that North Korean ruler Kim Jong-un "best not make any more threats to the US".

"They will be met with fire and fury and frankly power the likes of which the world has never seen before," Mr Trump said, in his first public comments since the news broke.

The US Defense Intelligence Agency has determined that North Korea possesses up to 60 nuclear weapons – some of which are small enough to fit on a long-range missile, The Washington Post reported. This number is more than double that predicted by most independent experts.

Japan's Defense Ministry has also concluded that "it is possible that North Korea has achieved the miniaturisation of nuclear weapons and has developed nuclear warheads."

In pictures: North Korea military drill Show all 8 1 /8 In pictures: North Korea military drill In pictures: North Korea military drill North Korea's leader Kim Jong Un watches a military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video

The North Korean regime tested two ICBMs - that they claimed were capable of hitting the US mainland - last month. The missiles were not believed to be capable of delivering a nuclear warhead at the time of launch, with experts split over their potential range.

The US retaliated by flying bombers over the Korean Peninsula and testing a missile of its own. American forces are also helping to deploy a US-made anti-missile defence system - THAAD - in South Korea. North Korea has often accused the US and South Korea of escalating tensions by conducting joint military drills.

Last week, the United Nations voted to impose an estimated $1bn in sanctions on North Korea. Praising the sanctions in an interview, US Ambassador Nikki Haley warned: "It is time for North Korea to realise, we are not playing anymore".

The North Korean government, however, responded by threatening to take “physical action” against the US.

“Packs of wolves are coming in attack to strangle a nation,” a statement broadcast on North Korean TV said. “They should be mindful that [North Korea's] strategic steps accompanied by physical action will be taken mercilessly with the mobilisations of all its national strength.”

North Korea said in a later statement that it is “carefully examining” a plan to strike the US Pacific territory of Guam with missiles. A spokesman for the Korean People's Army, in a statement carried by the North's state-run KCNA news agency, said the strike plan will be “put into practice” once leader Kim Jong-un makes a decision.

The consequences of any US strike against North Korea would potentially be catastrophic for South Koreans, Japanese and US military personnel within range of North Korean retaliatory strikes - let alone the possibility of civilian casualties.

US military and intelligence officials said any military action against North Korea could unleash a barrage of missiles and artillery in retaliation targeted at Seoul and US bases in South Korea and elsewhere that would likely claim hundreds of thousands of lives.

Several US officials have also said that military action is a possibility, although that is far from their first choice. National security adviser HR McMaster told MSNBC's Hugh Hewitt that the President is prepared to wage a "preventative war" against North Korea.

“[Mr Trump] said he’s not going to tolerate North Korea being able to threaten the United States,” Mr McMaster said. “...So of course, we have to provide all options to do that. And that includes a military option.”

US Defense Secretary Jim Mattis has warned of an “effective and overwhelming” response against North Korea if it chose to use nuclear weapons but has said any military solution would be “tragic on an unbelievable scale.”

Despite the tough talk, however, the majority of Americans say they aren't sure Mr Trump can resolve the conflict. Sixty-one per cent of Americans say they are “uneasy” about Mr Trump’s ability to handle the situation, according to a CBS News poll.

Others also have reservations about US action. Responding to Mr Trump's latest comments, Republican Senator John McCain said in an interview that “great leaders” don't threaten foes unless they're ready to act — and he's not certain President Trump is ready to act against North Korea.

Elsewhere, South Korea has reiterated further United Nations resolutions against Pyongyang could follow if it did not pull back. While Chinese Foreign Minister Wang Yi said the new UN resolution on exports showed China and the international community's opposition to North Korea's continued missile tests.

“Owing to China's traditional economic ties with North Korea, it will mainly be China paying the price for implementing the resolution,” China's foreign ministry in a statement on Tuesday, citing Mr Wang.