N Korea army vows 'merciless' response to US provocation

North Korea's army today vowed a 'merciless' response to any US provocation, as tensions soar over Pyongyang's nuclear programme and speculation mounts that it is preparing a fresh weapons test.

Pyongyang's rogue atomic ambitions have come into sharp focus in recent weeks, with United States President Donald Trump vowing a tough stance against the North and threatening unilateral action if China failed to help curb its neighbour's nuclear programme.

As hostilities in the region surge Trump has sent an aircraft carrier-led strike group to the Korean peninsula to press his point, while the North has launched a flurry of rockets.

In a statement on official news agency KCNA, the North's Korean People's Army said Trump had "entered the path of open threat and blackmail against the DPRK".

Citing Washington's recent missile strike on Syria, the typically bombastic statement boasted that US military bases in South Korea as well as Seoul's presidential Blue House "would be pulverized within a few minutes".

"The closer such big targets as nuclear powered aircraft carriers come (to the Korean peninsula), the greater would be the effect of merciless strikes," the statement added.

Earlier Friday Chinese foreign minister Wang Yi said a conflict over North Korea could break out "at any moment", warning there would be no winner in any war.

China, the country's sole major ally and economic lifeline, has come under increasing pressure to curb Pyongyang's militarism, but Beijing fears dramatic action could cause the regime's collapse, sending a flood of refugees across its borders and leave the US military on its doorstep.

Trump has repeatedly said he will prevent Pyongyang from its goal of developing a nuclear-tipped ballistic missile capable of reaching the mainland United States.

The US president also flexed his military muscle last week by ordering cruise missile strikes on a Syrian airbase the US believed was the origin of a chemical weapons attack on civilians in a northern Syria town.

On Thursday the US military dropped the biggest non-nuclear bomb it possesses on Afghanistan, targeting a complex used by the Islamic State group.

A White House foreign policy advisor said Friday the US is assessing military options in response to the North's weapons programmes, saying another provocative test was a question of "when" rather than "if".

There are reports of activity at a nuclear test site in North Korea ahead of Saturday's 105th anniversary of the birth of the country's founder Kim Il-Sung, fuelling speculation it could carry out a sixth test.