US President Donald Trump's tweets are adding fuel to a "vicious cycle" of tensions on the Korean Peninsula, North Korea's vice foreign minister told The Associated Press in an exclusive interview. The official added if the US shows any sign of "reckless" military aggression, Pyongyang is ready to launch a pre-emptive strike of its own.

Vice Minister Han Song Ryol said Pyongyang has determined the Trump administration is "more vicious and more aggressive" than that of Barack Obama. He added that North Korea will keep building up its nuclear arsenal in "quality and quantity" and said Pyongyang is ready to go to war if that's what Trump wants.

Tensions between Pyongyang and Washington go back to President Harry Truman and the 1950-53 Korean War, which ended in an armistice, not a peace treaty. North Korea is still technically at war with the South and the heat has been rising rapidly since Trump took office in January.

"Trump is always making provocations with his aggressive words," Han said. "It's not the DPRK but the US and Trump that makes trouble."

He added: "We will go to war if they choose."

A US State Department official said later Friday the US was aligning "all elements of national power" to get North Korea to abandon its nuclear and missile programs.

The official, who wasn't authorised to be quoted by name and demanded anonymity, lamented Pyongyang's "far too common and far too dangerous" provocations, and said Washington would work with international partners to cut the North's government off "from the rest of the world."

Han dismissed the suggestion Trump made last year during his presidential campaign that he was willing to meet Kim Jong Un, possibly over hamburgers.

"I think that was nothing more than lip service during the campaign to make himself more popular," Han said. "Now we are comparing Trump's policy toward the DPRK with the former administration's and we have concluded that it's becoming more vicious and more aggressive."

Han said North Korea changed its military strategy two years ago, when the reports of "decapitation strike" training began to really get attention, to stress pre-emptive actions.

"We've got a powerful nuclear deterrent already in our hands, and we certainly will not keep our arms crossed in the face of a US pre-emptive strike," he said. "Whatever comes from the US, we will cope with it. We are fully prepared to handle it."

China says tension over North Korea has to be stopped from reaching an "irreversible and unmanageable stage" as a US aircraft carrier group steams towards the region amid fears the North may conduct a sixth nuclear weapons test.

Concern has grown since the US Navy fired 59 Tomahawk missiles at a Syrian airfield last week in response to a deadly gas attack, raising questions about US President Donald Trump's plans for North Korea, which has conducted missile and nuclear tests in defiance of UN and unilateral sanctions.

The US has warned that a policy of "strategic patience" is over. US Vice President Mike Pence travels to South Korea on Sunday on a long-planned 10-day trip to Asia.

China, North Korea's sole major ally and neighbour which nevertheless opposes its weapons program, has called for talks leading to the denuclearisation of the Korean peninsula.

"We call on all parties to refrain from provoking and threatening each other, whether in words or actions, and not let the situation get to an irreversible and unmanageable stage," Chinese Foreign Minister Wang Yi told reporters in Beijing.

North Korea denounced the United States for bringing "huge nuclear strategic assets" to the region as the Carl Vinson strike group with a flag-ship nuclear- powered aircraft carrier steamed closer, and said it stood ready to strike back.