In a show of solidarity, two Japanese destroyers have joined the United States aircraft carrier the U-S-S Carl Vinson as it approaches waters off the Korean Peninsula.
North Korea has threatened it could sink the US carrier in a single strike.
But former presidential candidate and prominent US senator Marco Rubio is among those calling for North Korea to be stopped -- at almost any cost.
"We must do almost whatever it takes, just about anything, to prevent Kim Jong-un from acquiring a nuclear capability he can deliver against the mainland of the United States of America."
US president Donald Trump has spoken with both Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe about the escalating tensions.
Mr Xi says he hopes all sides will avoid doing anything to worsen relations.
He says China opposes anything that runs counter to United Nations Security Council resolutions.
Japan and the United States, meanwhile, have agreed to maintain close contact over North Korea.
Mr Abe says they are unified in their desire to see North Korea fall into line.
"We completely agreed to strongly demand that North Korea, who's been repeatedly dangerous and provocative, show restraint."
Along with South Korea, Japan is considered one of the primary targets of North Korean aggression.
China, on the other hand, is considered North Korea's main ally.
And former Australian Prime Minister Kevin Rudd says China has several options in dealing with North Korea.
"What are the options available to China? I think, if you started from the easier ones to the harder ones, it's, one, clamping down on North Korean coal exports to China, which currently provide the North Koreans with the bulk of their foreign exchange. China may or may not have started to do that -- the jury's out. The second is financial sanctions against the North (Koreans) to prevent them from going into the international market easily to purchase the things that they need. And, thirdly -- and this is the really hard one -- is to begin looking at how you would ratchet down the supply of Chinese oil into North Korea, because, if the North Koreans don't have oil, the wheels of their economy, and of their military capabilities, start to grind to a halt."
North Korea has also threatened a nuclear strike on Australia if it remains an ally of the United States.
The acting head of the Strategic and Defence Studies Centre in Canberra, Professor John Blaxland, says Australia must act with caution.
"Within two to four years, the North Koreans should be able to bring together the nuclear-weapons technology miniaturised to be assembled on the tip of a ballistic missile, bring the ballistic-missile technology together and have the long-range capability to project nuclear weapons to reach the United States, potentially reach Australia as well."
As North Korean leader Kim Jong-un visited a military-operated pig farm, another US citizen was reported to have been detained in the country.
An accounting professor at a private North Korean university, Tony Kim, has been taken into custody at an airport as he tried to leave North Korea with his wife.
That takes the total number of US citizens held in North Korea to at least three.
Former US ambassador to the United Nations Bill Richardson says that is at least three US bargaining chips North Korea now has.
It comes as North Korea is about to celebrate the 85th anniversary of its people's army -- another traditional opportunity to show off its strength.
