The US Navy said Saturday it had sent a carrier-led strike group to the Korean peninsula in a show of force against North Korea's "reckless" nuclear weapons program.
The move will raise tensions in the region and comes hard on the heels of a US missile strike on Syria that was widely interpreted as putting Pyongyang on warning over its refusal to abandon its nuclear ambitions.
North Korea denounced Thursday's strike as an act of "intolerable aggression" and one that justified "a million times over" the North's push toward a credible nuclear deterrent.
"US Pacific Command ordered the Carl Vinson Strike Group north as a prudent measure to maintain readiness and presence in the Western Pacific," said Commander Dave Benham, spokesman at US Pacific Command.
"The number one threat in the region continues to be North Korea, due to its reckless, irresponsible and destabilising program of missile tests and pursuit of a nuclear weapons capability," he told AFP, in an unusually forceful statement.
Originally scheduled to make port calls in Australia, the strike group - which includes the Nimitz-class aircraft supercarrier USS Carl Vinson is now headed from Singapore to the Western Pacific Ocean.
Pyongyang is on a quest to develop a long-range missile capable of hitting the US mainland with a nuclear warhead, and has so far staged five nuclear tests, two of them last year.
Expert satellite imagery analysis suggests it could well be preparing for a sixth, with US intelligence officials warning that Pyongyang could be less than two years away from developing a nuclear warhead that could reach the continental United States.
North Korea on Wednesday fired a medium-range ballistic missile into the Sea of Japan ahead of a US-China summit.
In February the North simultaneously fired four ballistic missiles off its east coast, three of which fell provocatively close to Japan, in what it said was a drill for an attack on US bases in the neighbouring Asian country.
Last August Pyongyang also successfully test-fired a submarine-launched ballistic missile 500km towards Japan, far exceeding any previous sub-launched tests, in what the North's leader Kim Jong-Un hailed as the "greatest success."
A nuclear-capable SLBM system would take the North's threat to a new level, allowing deployment far beyond the Korean peninsula and a "second-strike" capability in the event of an attack on its army bases.
Removing Al-Assad a top US priority
Meantime, the removal of Syrian President Bashar al-Assad is a priority for Donald Trump, says the US Ambassador to the UN.
Nikki Haley said the removal of al-Assad, removing Iranian influence in Syria and defeating the Islamic State terrorist group are the priorities for the US President.
"We don't see a peaceful Syria with Assad in there," Haley told CNN.
The comments represented a departure from what Haley said before the US hit a Syrian air base with 59 Tomahawk missiles on Thursday in retaliation for a chemical weapons attack by al-Assad's forces on Syrian civilians.
Australia's Prime Minister Malcolm Turnbull also doubted if al-Assad could play any part of a peaceful solution to the six-year civil war.
"I have grave doubts as to whether he can have any continuing role in the settlement. The crimes he has committed against his own people are so enormous," Mr Turnbull said from Port Moresby, Papua New Guinea.
"His actions, his horrendous, criminal actions, gassing women and children, babies, that surely disqualifies him from a continuing role."
President Trump ordered the missile strike after watching television images of infants suffering from chemical weapons injuries.
"You pick and choose your battles and when we're looking at this, it's about changing up priorities and our priority is no longer to sit there and focus on getting Assad out," Haley told reporters on March 30, just days before more than 85 Syrian civilians died from chemical weapons injuries.
New air strikes have targeted the town in Syria devastated by the chemical attack, with Russian planes believed to be responsible.
It wasn't immediately clear who conducted the strikes on Khan Sheikhoun, which was hit on Friday and Saturday, though only Russian and Syrian regime aircraft have been bombing that rebel-held area.
At least four civilians were killed.
Defence Minister Marise Payne said that the US was keeping Australia informed of developments and had not asked for additional resources, as she again urged Russia to work with the Assad regime to find a solution to the endless conflict.
"I will be meeting with senior members of the coalition again in the coming weeks and we will expect to discuss these activities further,' she told ABC TV.
Senator Payne said Australia was already contributing significantly in advising and assisting personnel in Iraq.
"I know that is acknowledged by Iraq particularly, by the United States and other members of the coalition."
The US is vowing to keep up the pressure on Syria after the intense night-time wave of missile strikes from US ships, despite the prospect of escalating Russian ill will that could further inflame one of the world's most vexing conflicts.
US Secretary of State Rex Tillerson is due to meet Russian Foreign Minister Sergei Lavrov in Moscow on Wednesday.
Standing firm, the Trump administration has signalled new sanctions would soon follow the missile attack, and the Pentagon was even probing whether Russia itself was involved in the chemical weapons assault that compelled President Trump to action. The attack against a Syrian air base was the first US assault against the government of al-Assad.
Mr Trump also tweeted an explanation as to why Syrian planes were already able to take off from the air base that was targeted in the US air strikes.
"The reason you don't generally hit runways is that they are easy and inexpensive to quickly fix (fill in and top)!" he wrote, defending the US targets.
It comes as North Korea said the US missile strikes on Syria were an "intolerable act of aggression" that "proves a million times over" that strengthening its nuclear program was the right choice, state media reported Saturday.
The comments were Pyongyang's first since Mr Trump ordered the strikes on an air base in the war-wracked country on Thursday.
"The US missile attack against Syria is a clear and intolerable act of aggression against a sovereign state and we strongly condemn it," KCNA news agency quoted an unnamed spokesman for the North Korean foreign ministry as saying.
"The reality of today shows that we must stand against power with power and it proves a million times over that our decision to strengthen our nuclear deterrence has been the right choice." Analysts had earlier said the strikes contained a clear message for Pyongyang that the US was not afraid to exercise the military option, and there had been speculation as to how the North would respond.
Mr Trump has recently threatened unilateral action against Pyongyang if Beijing fails to help curb its neighbour's nuclear weapons program.
However, Pyongyang's response suggested the reclusive state was determined to continue with its nuclear weapons program.
"Swaggering as a superpower, the US has been picking only on countries without nuclear weapons and the Trump administration is no exception," the foreign ministry spokesman said, according to KCNA.
A furious Russia also declared Mr Trump's strike on Syria put the United States "one step away" from war as it directed a warship towards the two US destroyers that launched Thursday's missile attack.
The US stood firm behind its retaliatory deployment of 59 Tomahawks on Shayrat Airbase, from where Syrian government forces launched a devastating chemical attack last Tuesday that horrified the world and killed at least 87.
Among those slaughtered were 27 children, and Mr Trump said footage of them struggling to breathe spurred his decision to launch the first military action of his presidency and the first US intervention into Syria's bloody six year civil war.
While Mr Trump's decisive strike has the support of nations including Saudi Arabia, Australia, Britain and France.
However, Syria and its closest allies Russia and Iran have expressed outrage at the escalation.
But the US doubled down, saying it was investigating whether Russia was involved in the chemical strike as it foreshadowed new economic sanctions against Syria, where fighting has killed more than 400,000 and displaced 11 million people.
"We are prepared to do more, but we hope that will not be necessary," US ambassador to the United Nations Nikki Haley told an emergency meeting of the UN Security Council.
A spokesman for Russian President Vladimir Putin warned the strikes dealt "a significant blow" to relations between Moscow and Washington. Russia's deputy ambassador, Vladimir Safronkov, told the UN it was a "flagrant violation of international law and an act of aggression" whose "consequences for regional and international security could be extremely serious."
And Russia's Prime Minister Dmitry Medvedev claimed Mr Trump had been "one step away from military clashes with Russia".
Mr Trump's show of strength came during one of the most important meetings of his young presidency, as he hosted Chinese President Xi Jinping and his wife at the Florida golf resort dubbed the "winter White House".
The first high stakes summit between the two superpowers was to discuss trade, security in the South China Sea and how to counter the nuclear threat of an increasingly aggressive North Korea.
Mr Trump said in a brief appearance before reporters that he and Mr Xi made "tremendous progress" in their first face-to-face talks and that he believe "lots of very potentially bad problems will be going away".
The missile strike was one of several options considered by Mr Trump and his senior security advisers, who also canvassed targeting the palace of dictator Bashar al-Assad, according to Reuters.
White House press secretary Sean Spicer said yesterday the air strikes were the result of a "72-hour evolution", which marked a reversal of Mr Trump's previous position, stated as recently as this week, that the US would not interfere in Syria.
Syrian media said the strikes on the air base in Homs province - just after 3.30am Friday local time - killed at least seven soldiers.
US officials said at least 20 jets were destroyed, as well as infrastructure.
Within hours, Russia reportedly sent its most advanced Black Sea frigate into the Eastern Mediterranean, towards the destroyers USS Ross and USS Porter.
The Admiral Grigorovich RFS-494 crossed through the Bosphorus Strait from the Black Sea, according to an unnamed US defence official who spoke to Fox News.
Russian news agency TASS said the ship had recently taken part in a joint exercise with Turkish ships and was bound for the Syrian port of Tartus on a routine voyage.