Japanese fighters conduct joint air drills with US supersonic bombers close to the Korean peninsula as reports emerge of Pyongyang miniaturising a nuclear warhead.
North Korea said on Wednesday it is considering plans for a missile strike on the US Pacific territory of Guam, just hours after President Donald Trump told the North that any threat to the United States would be met with "fire and fury."
The sharp increase in tensions rattled global financial markets and prompted warnings from US officials and analysts not to engage in rhetorical slanging matches with North Korea.
Pyongyang said it was "carefully examining" a plan to strike Guam, home to a US military base that includes a submarine squadron, an air base and a coast guard group.
A Korean People's Army spokesman said in a statement carried by state-run KCNA news agency the plan would be put into practise at any moment once leader Kim Jong-Un makes a decision.
Uh I'm seeing too many "what is Guam?" tweets. GUAM:— Michelle Ye Hee Lee (@myhlee) August 8, 2017
-Has two US military bases
-No this isn't the 1st time NK threatened Guam
In another statement citing a different military spokesman, North Korea also accused the US of devising a "preventive war" and said any plans to execute this would be met with an "all-out war wiping out all the strongholds of enemies, including the US mainland".
"Guam remains safe, and I am confident in the ability of US defences to protect our island and allies in the region," Congresswoman for the US Pacific territory of Guam Madeleine Z Bordallo said in a statement on Wednesday.
Bordallo called on President Donald Trump to show "steady leadership" and work with the international community to de-escalate tensions and stop North Korea advancing its weapons programme.
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.
Trump issued his strongest warning yet to North Korea in comments to reporters in New Jersey on Tuesday. "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 said.
Message to North Korea
US Secretary of State Rex Tillerson said on Wednesday that President Donald Trump was trying to send a strong message to North when he said it would face "fire and fury" if it threatened the US.
Speaking to reporters before landing in Guam, Tillerson said North Korea's rhetoric had ratcheted up in the face of international opposition to its nuclear program.
"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," he said.
Nuclear tipping point?
North Korea has made no secret of its plans to develop a nuclear-tipped missile able to strike the US and has ignored international calls to halt its nuclear and missile programmes.
Pyongyang says its intercontinental ballistic missiles (ICBMs) are a legitimate means of defence against perceived US hostility. It has long accused the US and South Korea of escalating tensions by conducting military drills.
US stocks closed slightly lower after Trump's comment and S&P; stock futures slipped further in Asian trade, while a widely followed measure of stock market anxiety ended at its highest in nearly a month.
"North Korea has no intentions of backing down. Tensions will continue to mount and could eventually develop into a black swan event that the markets are not prudently considering," Steve Hanke, professor of Applied Economics at the Johns Hopkins University, told the Reuters Global Markets Forum.
An upward trajectory of tension
The US has remained technically at war with North Korea since the 1950-53 Korean conflict ended in an armistice rather than a peace treaty.
Seoul is home to roughly 10 million people, within range of massed North Korean rockets and artillery, which would be impossible to destroy in a first US strike.
Tens of thousands of US troops remain stationed in South Korea and in nearby Japan, the only country to have been attacked with nuclear weapons. Wednesday marked the 72nd anniversary of the atomic bombing of the city of Nagasaki by the US.
Tensions in the region have risen since North Korea carried out two nuclear bomb tests last year and two ICBM tests last month.
The UN Security Council unanimously imposed new sanctions on North Korea on Saturday over its continued missile tests.
Japanese fighters conducted joint air drills with US supersonic bombers in Japanese skies close to the Korean peninsula on Tuesday, Japan's Air Self Defence Force said.
On Monday, two US B-1 bombers flew from Guam over the Korean Peninsula as part of its "continuous bomber presence", a US official said, in a sign of the strategic importance Guam holds.
The alert status at Andersen Airforce Base on Guam had not been changed as of Wednesday morning, according to the duty officer at the base's public affairs office.
Republican US Senator John McCain said Trump should tread cautiously when issuing threats to North Korea unless he is prepared to act.
NEW: Sen. McCain reacts to Trump's North Korea threat on local Arizona radio: pic.twitter.com/CGvYGPsHLr— Marianna Sotomayor (@MariannaNBCNews) August 8, 2017
"I take exception to the president's comments because you've got to be sure you can do what you say you're going to do," he said in a radio interview.
Former US diplomat Douglas Paal, now with the Carnegie Endowment for International Peace think tank in Washington, said Trump should not get into a war of words with Pyongyang.
"It strikes me as an amateurish reflection of a belief that we should give as we get rhetorically. That might be satisfying at one level, but it takes us down into the mud that we should let Pyongyang enjoy alone," said Paal, who served as a White House official under previous Republican administrations.