Vice-President Mike Pence has warned North Korea not to test US military might by pursuing its nuclear weapons programme, citing recent strikes in Syria and Afghanistan as proof of American "strength and resolve".

The stark warning, delivered in Seoul after the United States Vice-President went to the military demarcation line that separates the two Koreas, could revive speculation that the White House is considering military action against the regime of Kim Jong Un.

Pence said the Trump Administration wants to persuade North Korea to abandon its nuclear weapons "through peaceful means", but he repeated the Administration's warning that "all options are on the table".

In Washington, President Donald Trump told CNN at the annual White House Easter Egg Roll that North Korea has "gotta behave".

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White House spokesman Sean Spicer said Trump would not be "drawing red lines in the sand" with North Korea. "He holds his cards close to the vest, and I think you're not going to see him telegraphing how he's going to respond to any military or other situation going forward," Spicer said. "I think that the action that he took in Syria shows that when appropriate, this President will take decisive action."

Spicer later cautioned reporters not to "make too much" of an analogy between Syria and North Korea.

A State Department official said yesterday that the US would continue trying to further isolate North Korea economically, politically and diplomatically.

The pressure would keep ratcheting up until Pyongyang stops conducting missile tests and demonstrates it is willing to engage in negotiations, said Susan Thornton, the acting Assistant Secretary for East Asian and Pacific Affairs.

"We're looking for some kind of signal that they realise the current status quo is unsustainable," she said.

Pence, who yesterday travelled to Japan, arrived in South Korea just hours after North Korea launched its latest ballistic missile - which exploded within a few seconds - and amid a weekend of fanfare in North Korea, during which the regime showed off what appeared to be new missiles. There, during a trip to the demilitarised zone between North and South Korea and later in remarks to journalists, he issued strong warnings to Pyongyang.

U.S. Vice President Mike Pence. Photo / AP
U.S. Vice President Mike Pence. Photo / AP

"Just in the past two weeks, the world witnessed the strength and resolve of our new President in actions taken in Syria and Afghanistan," Pence said after delivering a statement to the media alongside Hwang Kyo Ahn, South Korea's acting President. Neither took questions.

"North Korea would do well not to test his resolve or the strength of the armed forces of the United States in this region," Pence said.

Earlier this month, on Trump's command, the US military launched 59 cruise missiles at a Syrian military airfield in retaliation for a chemical attack that killed scores of civilians.

Then, less than a week later, the US military dropped a 10,300kg bomb - the largest non-nuclear bomb ever used in combat by the US - on Isis (Islamic State) forces in eastern Afghanistan.

With Kim Jong Un's regime conducting a steady stream of ballistic missile launches and signs of activity around its nuclear test site, the Trump Administration has raised the rhetoric on possible military action to stop it in its tracks.

But any strikes against the North would probably bring the US into a diplomatic crisis with China, the North's main economic lifeline.

In Beijing, Foreign Ministry spokesman Lu Kang called for international talks with North Korea to ease tensions.

Just in the past two weeks, the world witnessed the strength and resolve of our new President in actions taken in Syria and Afghanistan. North Korea would do well not to test his resolve or the strength of the armed forces of the United States in this region.

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Russia, too, warned that the Trump Administration was on what Foreign Minister Sergei Lavrov called a "very risky path". "I hope there will be no unilateral actions like those we saw recently in Syria," Lavrov told reporters in Moscow.

Both US Secretary of State Rex Tillerson, who visited South Korea last month, and Pence have stated that "strategic patience" - the Obama-era policy of putting pressure on North Korea and waiting for it to return to negotiations - is over and that military action is an option to make North Korea desist.

The US Navy's decision to reroute an aircraft carrier strike group destined for Australia to the "western Pacific" sparked speculation it was heading to the Korean Peninsula, adding to the jitters in the region.

The plan has been controversial in South Korea, with some worried that it would make the South more of a target for North Korean missiles and others concerned about economic revenge being exacted by China.

The frontrunner to replace ousted President Park Geun Hye in a snap presidential election to be held May 9, progressive politician Moon Jae In, has promised to review the previous Government's decision to host the US anti-missile system Thaad (Terminal High Altitude Area Defence).

Beijing strongly objects to Thaad because it worries that the US will use its batteries' associated radar to snoop on China. China has imposed a painful economic boycott on South Korean exports and is making life difficult for South Korean companies in China.

Pence said the US would press ahead with the Thaad deployment and added: "The better path would be for China to address the North Korean threat that is actually making such defensive measures necessary."