North Korea's sprint towards full-fledged nuclear statehood accelerated sharply in 2017, raising fears about a devastating atomic exchange to levels not seen since the Cold War.

An increasingly-belligerent Pyongyang -- and volatile US rhetoric -- dominated the world agenda and looks set to do the same next year as the international community struggles to contain the North's nuclear and missile ambitions.

Multiple sets of UN sanctions failed to stop Pyongyang from carrying out its sixth and most powerful nuclear test -- which it said was a hydrogen bomb -- in September.

North Korea has also tested increasingly longer-range intercontinental ballistic missiles (ICBMs) throughout 2017, and claims it can now strike the US mainland.

US President Donald Trump has responded to each test with his own amplified declarations, threatening to "totally destroy" Pyongyang and taunting Kim Jong-Un, saying the North Korean leader was on "a suicide mission".

But far from persuading Kim to give up his nuclear drive, analysts say Trump's tough talk may have prompted the North Korean leader to accelerate his dangerous quest.

Vipin Narang, a professor at the Massachusetts Institute of Technology, said vulnerable states respond to external threats of force by seeking their own arsenals.

"The best way is to just sprint to a point where you raise the cost of that potential action by signalling, 'I have a lot of nuclear weapons'," Narang told AFP.

"It's impressive and scary how fast they were able to get all these pieces in place," he added.

North Korea says it needs nuclear weapons to defend itself against a hostile America and that its priority is its own survival. Critics say it seeks to reunify the peninsula -- divided by a demilitarised zone since the end of the 1950-53 Korean war -- by force.

- Siren call -

In response to North Korea's recent strides, the United States and its allies have increased their demonstrations of military might, including more frequent flights of American bombers over the Korean peninsula.

At the same time, top Trump administration officials have repeatedly warned of military options, stoking concerns of miscalculation that could rapidly spiral into conflict.

Van Jackson, a defence expert at the Victoria University of Wellington, said the heightened tensions combined with the growing sophistication of the North's arsenal have increased the chances of an "inadvertent nuclear war" to their highest since the Cold War.

"If North Korea believes the US is going to invade or decapitate the Kim regime, it will have strong incentives to launch a nuclear first strike," Jackson said.

And in countries within reach of the North's missiles, the current confrontation has unleashed fears of a nuclear war which could kill millions of people.

Nervous Japanese have been scrambling to prepare against a potential attack, some even opting to build bomb shelters in their homes and offices.

In South Korea, calls have grown for the country to develop its own nuclear weapons, which would put its decades-old security alliance with the United States in jeopardy, amid doubts whether Washington would be willing to trade "Seoul for Seattle".

Sirens blared across the islands of Hawaii earlier this month as the US state tested its nuclear attack warning system, revived for the first time since the Cold War.

- Policy failure -

Many analysts say Washington must open talks with the North to defuse tensions -- but that remains a challenge.

The North has always said its nuclear weapons are not up for negotiation, and that it will only deal with the United States from a position of equality -- as a nuclear state.

Washington has long insisted that it will not accept a nuclear-armed North Korea and Pyongyang must take concrete steps towards disarmament before any talks, which should lead to its denuclearisation.

That stance seemed to soften this month when Secretary of State Rex Tillerson said for the first time that discussions could take place "without preconditions" -- but the White House said its policy had not changed.

The North declared this month it had reached nuclear statehood with its new Hwasong-15 ICBM, which can carry a "super heavy warhead" to the US mainland.

"I find the entire argument about 'not accepting' North Korean nuclear weapons to be strange," said Joshua Pollack, a senior research associate at the Middlebury Institute of International Studies at Monterey.

"Saying certain words, or not saying them, won't change the reality," Pollack told AFP.

Still, sitting down with a "nuclear" North Korea would mean accepting a huge policy failure by the United States of not stopping the regime in the first place.

The longer Washington waits, the higher the diplomatic price of dealing with an already complicated problem will go, said Joel Wit, senior fellow at the US-Korea Institute at Johns Hopkins University.

Wit, who negotiated with North Korea under the Clinton and Bush administrations, said that Pyongyang used to have only "clunky rockets".

"We used to laugh at them and say yeah, this isn't serious," he said of the US.

"Now we see it is serious, and the point is, the price has gone way up and it's going to be a tough nut to crack."

Source: AFP