As tensions escalated, Pyongyang said on Wednesday it was “carefully examining” a plan to strike Guam, the site of a US military base.

A North Korean military spokesman, in a statement carried by state-run KCNA news agency, said the plan would be put into practice once leader Kim Jong Un made a decision.

In another statement citing a different military spokesman, North Korea said it could carry out a pre-emptive operation if there were signs of a US provocation.

Washington has warned it is ready to use force if need be to stop North Korea’s ballistic missile and nuclear programs but it prefers global diplomatic action, including sanctions.

“North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen,” Trump told reporters at the Trump National Golf Club in Bedminster, New Jersey.

The UN Security Council unanimously imposed new sanctions on North Korea on Saturday over its continued missile tests, that could slash the reclusive country’s $A3.8 billion annual export revenue by one-third.

North Korea has made no secret of plans to develop a nuclear-tipped missile able to strike the US and has ignored international calls to halt its nuclear and missile programs.

It says its intercontinental ballistic missiles are a legitimate means of defence against perceived US hostility.

Tensions have risen since North Korea carried out two nuclear bomb tests in 2016 and two ICBM tests in July.

Republican US Senator John McCain said Trump should tread cautiously when issuing threats to North Korea unless he was prepared to act.

“I take exception to the president’s comments because you got to be sure you can do what you say you’re going to do,” he said in a radio interview.

Trump’s warning came as The Washington Post reported that North Korea had successfully produced a miniaturised nuclear warhead that could fit inside its missiles, according to a US intelligence assessment.

Washington has warned it is ready to use force if need be to stop North Korea’s weapons ballistic missile and nuclear programs but has said it prefers global diplomatic action, including sanctions.

The consequences of a US strike would potentially be catastrophic for South Koreans, Japanese and US military personnel within range of North Korean retaliatory strikes.

Earlier on Tuesday, Japan’s Defence Ministry said “it is conceivable that North Korea’s nuclear weapons program has already considerably advanced and it is possible that North Korea has already achieved the miniaturisation of nuclear weapons and has acquired nuclear warheads.”

The UN Security Council unanimously imposed new sanctions on North Korea on Saturday over its continued missile tests that could slash the reclusive country’s $3 billion annual export revenue by a third.

North Korea said the sanctions infringed its sovereignty and it was ready to give Washington a “severe lesson” with its strategic nuclear force in response to any US military action.

North Korea has made no secret of its plans to develop a nuclear-tipped missile capable of striking the United States and has ignored international calls to halt its nuclear and missile programmes.

North Korea says its intercontinental ballistic missiles (ICBMs) are a legitimate means of defence against perceived US hostility. It has long accused the United States and South Korea of escalating tensions by conducting military drills.

US stocks fell, with the S&P 500 at a session low after Trump’s comment, while a widely followed measure of stock market anxiety spiked higher and was on track to close at a one-month high. The US dollar index slightly pared gains as the safe-haven yen strengthened against the US currency.

– Reuters