America’s nuclear arsenal is now far stronger and more powerful than ever before, says President; Pyongyang warns of “all-out war” if U.S. attacks.

President Donald Trump followed up his incendiary warning to North Korea against threatening the U.S. with a boast on Wednesday about the strength of the American nuclear arsenal, although he expressed hope it would not need to be used.

Mr. Trump's Twitter messages about the nuclear arsenal came after North Korea said it was considering plans for a missile strike on the U.S. Pacific territory of Guam. That in turn followed Mr. Trump's comments on Tuesday that any North Korean threat to the U.S. would be met with “fire and fury.”

“My first order as President was to renovate and modernize our nuclear arsenal. It is now far stronger and more powerful than ever before,” Mr. Trump tweeted. “Hopefully we will never have to use this power, but there will never be a time that we are not the most powerful nation in the world!”

The sharp increase in tensions between a country that has one of the world’s largest nuclear arsenals and an aspiring nuclear power rattled financial markets and prompted U.S. Secretary of State Rex Tillerson to try to play down the rhetoric.

While Mr. Trump said the nuclear arsenal was more powerful than ever before, U.S. officials say it takes decades to actually modernise nuclear weapons, a move already under way under President Barack Obama’s administration, and there are treaties that regulate nuclear expansion. The Trump administration is still conducting a nuclear posture review.

Strong message

Shortly before Mr. Trump’s remarks on the nuclear arsenal, Mr. Tillerson landed in Guam for a previously scheduled visit after telling reporters he did not believe there was an imminent threat from North Korea and that “Americans should sleep well at night.” Mr. Tillerson said that with his “fire and fury” warning, the U.S. President was trying to use the kind of language that would resonate with North Korean leader Kim Jong-un. North Korea regularly threatens to destroy the U.S.

“What the President is doing is sending a strong message to North Korea in language that Kim Jong Un would understand, because he doesn't seem to understand diplomatic language," Tillerson said.

Earlier on Wednesday, North Korea said it was “carefully examining” a plan to strike Guam, which is home to about 163,000 people and a U.S. military base that includes a submarine squadron, an airbase and a Coast Guard group.

The plan would be put into practice at any moment, once Mr. Kim made a decision, a Korean People's Army spokesman said in a statement carried by state-run KCNA news agency.

Guam Governor Eddie Calvo dismissed the threat and said the island was prepared for “any eventuality” with strategically placed defences. He said he had been in touch with the White House and there was no change in the threat level. “Guam is American soil... We are not just a military installation,” Mr. Calvo said in an online video message.

Preventive war

North Korea, which is pursuing missile and nuclear weapons programmes in defiance of UN Security Council resolutions, also accused the U.S. of devising a “preventive war” and said in another statement that any plans to execute this would be met with an “all-out war, wiping out all the strongholds of enemies, including the U.S. mainland.”

Washington has warned it is ready to use force if needed to stop North Korea’s ballistic missile and nuclear programmes but that it prefers global diplomatic action, including sanctions. The UN Security Council unanimously imposed new sanctions on North Korea on Saturday.

Mr. Trump issued his strongest warning yet for North Korea in comments to reporters in New Jersey on Tuesday, saying that “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.”

John McCain, like Mr. Trump a Republican and heads of the Armed Forces Committee in the U.S. Senate, said on Tuesday night the President should tread cautiously. “You’ve got to be sure you can do what you say you’re going to do,” he said in a radio interview.

The top Democrat in the House of Representatives, Nancy Pelosi, called Trump’s “fire and fury” comments “recklessly belligerent.”

Call for talks

China, North Korea’s closest ally despite Beijing’s anger at Pyongyang’s missile and nuclear programmes, described the situation as “complex and sensitive,” and urged calm and a return to talks.

“China calls on all sides to uphold the main direction of a political resolution to the Korean Peninsula nuclear issue, and avoid any words or actions that may intensify the problem and escalate the situation,” the government said in a statement sent to Reuters, repeating its customary stance.

Great concern

Catherine Ray, a spokeswoman for the European Union’s executive arm in Brussels, told a news briefing on Wednesday the situation in North Korea is of “great concern” and called on the North to “refrain from any further provocative action”.

North Korea has made no secret of its plans to develop a nuclear-tipped missile able to strike the U.S. and has ignored all calls to halt its weapons programmes.

Pyongyang says its intercontinental ballistic missiles are a legitimate means of defence against perceived U.S. hostility, including joint military drills with South Korea.

South Korea and the U.S. remain technically still at war with North Korea after the 1950-53 Korean conflict ended with a truce, not a peace treaty.