Trump boasts of U.S. nuclear arsenal after 'fire and fury' warning to North Korea

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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 Trump's comments on Tuesday that any North Korean threat to the United States 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," 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!"

US President Donald Trump.

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 Trump said the nuclear arsenal was more powerful than ever before, U.S. officials say it takes decades to actually modernize 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.

Shortly before Trump's remarks on the nuclear arsenal, 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."

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 United States.

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.