North Korea is years beyond the nuclear “breakout” the US so fears in Iran. Pyongyang’s first nuclear test was more than a decade ago. Four more have followed with yields up to twice the size of the Hiroshima bomb. The country is believed to have around twenty fission bombs and to be progressing along the path to a much larger hydrogen bomb. Moreover, the regime is consistently making faster progress on missile technology than US intelligence has expected, including the stunning July 4 test of what appears to be a bona fide intercontinental ballistic missile (ICBM). North Korea’s shorter-range missiles can now be fired from mobile launchers rather than fixed sites, and fueled with solid rather than liquid fuel. Both of these advances make preparation for a missile launch much quicker and harder to detect. The crucial remaining unknowns are how long it will take Pyongyang to perfect an ICBM capable of reaching the continental US and to miniaturize nuclear weapons so that they can be delivered atop a missile.
Above all, in neither country is there an attractive military option. North Korea is capable of inflicting millions of casualties on South Korea with conventional heavy artillery before those guns could be silenced. Negotiation is therefore unavoidable. This means that a winner-take-all goal (comparable to the zero-enrichment position vis-à-vis Iran) is unachievable. Time spent pursuing one will be wasted.
Instead, as with Iran, what can be achieved has to be calibrated against present circumstances. In view of Pyongyang’s large nuclear arsenal and advanced missile delivery systems, the long-standing US insistence that North Korea agree to complete denuclearization as a precondition to talks is far out of date and must be dropped.
Ultimately, then, the only approach that might work is one that has not yet been tried: a joint effort by the US and China. As an eventual outcome, both sides’ interests would be met by a unified, denuclearized, neutral Korea. While this end state is not hard to define, the process of getting there would be tortuous and require a degree of mutual trust between Washington and Beijing that does not now exist. Small, confidence-building steps would be needed over a long period. North and South Korea would have to find an acceptable basis for reunification—overcoming mountains of difficulty in bringing together a dictatorship that is nothing without its weapons and a democracy whose economy is more than one hundred times larger. North–South agreements signed in 1991 and 2000 point to a confederation between the two states as the means of starting the process.
The effort would take years. In the meantime, the US and the world will have to depend on a determined defense and, more importantly, deterrence. Rhetorical bluster and military gestures—like firing off missiles in response to North Korean tests—only confirm the regime’s paranoia and undermine US credibility. Pyongyang will not be frightened into changing direction at this late date. Washington can and should tighten sanctions on Chinese banks and companies trading with North Korea, and continue to pressure Beijing into taking a tougher stance. But it would be a huge mistake to make this issue the sole test of the US–China relationship, as President Trump repeatedly suggests he will do. That would be to trade one strategic threat for two.
North Korea's leader Kim Jong-un has said a nuclear launch button is "always on my table" and warned the US it will never be able to start a war.
In a televised new year speech, he said the entire US was within range of North Korean nuclear weapons, adding: "This is reality, not a threat."
But he also offered a potential olive branch to South Korea, suggesting he was "open to dialogue".
North Korea may also send a team to the Winter Olympics in Seoul, he said.
When asked by reporters to respond to Mr Kim's latest threats, US President Donald Trump said, "We'll see, we'll see".
He was speaking at the sidelines of New Year's Eve celebrations at his Mar-a-Lago resort in Florida.
North Korea has come under increased criticism and sanctions over the past year because of its nuclear weapons programme and repeated testing of conventional missiles.
It claims to have a fully deployable nuclear weapon, though there is still some international scepticism about its true capacity to carry out such an attack.
In his speech, Mr Kim re-emphasised his focus on the weapons programme, but implied the country still has a few stages left to go before achieving its ambitions. North Korea must "mass-produce nuclear warheads and ballistic missiles and speed up their deployment", he said.
He also said they would not use their weapons unless they felt that peace was threatened.
While his language against the US remained tough, Mr Kim did not employ his typically antagonistic tone when speaking about his neighbours in South Korea.
"The year 2018 is a significant year for both the North and the South, with the North marking the 70th anniversary of its birth and the South hosting the Winter Olympics.
"We should melt the frozen North-South relations, thus adorning this meaningful year as a year to be specially recorded in the history of the nation," he said.
A spokesperson for the South Korean president said their office had "always stated our willingness to talk with North Korea at anytime and anywhere".
"We hope the two Koreas will sit down and find a solution to lower tensions and establish peace on the Korean peninsula."
Youngshik Daniel Bong, a research fellow at Yonsei Institute for North Korean Studies, told the BBC that addressing the South was a marked change from the norm for Mr Kim.
"North Korea usually ignores South Korea, maintaining the position that as a 'nuclear power' it will deal with the US on its own," said Mr Bong. "It appears that by engaging the South, he hopes to create an estrangement between South Korea and the US."
The analyst also said that Mr Kim could be seeking to improve ties to offer some respite from the growing economic pressures from the recent UN sanctions.
Mr Kim also said he would also consider sending a delegation to the Games in Pyeongchang, South Korea, in February - a gesture which South Korea has previously suggested would be welcome.
"North Korea's participation in the Winter Games will be a good opportunity to show unity of the people and we wish the Games will be a success," he said.
"Officials from the two Koreas may urgently meet to discuss the possibility."
The president of the PyeongChang Games' organising committee, Lee Hee-beom, told South Korea's news agency Yonhap he was delighted to hear of the potential participation.
"[The committee] enthusiastically welcomes it. It's like a New Year's gift," he said.
The only two North Korean athletes who qualified for the Games are figure skaters Ryom Tae-Ok and Kim Ju-Sik.
Although the North has missed the official deadline to confirm their participation, the skaters could still compete with an invitation by the International Olympic Committee.
South Korea's President Moon Jae-in last month suggested delaying an annual joint military drill with US troops until after the Games. The North usually denounces any such exercises as a rehearsal for war.
Robert Kelly, a political science professor at South Korea's Pusan National University, told the BBC that the Winter Olympics statement was "a smart move from North Korea" as it positioned Mr Kim's regime as moving towards its neighbours while the US was seeking to isolate it.
South Korea has offered high level talks with North Korea on 9 January to discuss its possible participation in the 2018 Winter Olympic Games.
It comes after the North's leader Kim Jong-un said he was considering sending a team to Pyeongchang in South Korea for the Games in February.
He said the two sides should "urgently meet to discuss the possibility".
South Korea's president said earlier he saw the offer as a chance to improve the highly tense relationship.
South Korean Unification Minister Cho Myoung-gyon proposed on Tuesday that representatives could meet at Panmunjom, the so-called "truce village
I don't think everything about America's approach was ham fisted,
I'd really like to see the two Koreas solve this without the USA trying to manage everything in its usual ham-fisted way.
Quote:I don't think everything about America's approach was ham fisted,
You don't think Bill Clinton's failed attempt with NK and their nuke program 20 years ago was ham fisted? It is pretty much the reason we are in this mess in the first place, and we will be in the same place with Iran in 20 years thanks to Obama.
What is needed is a drastic change in our approach to the Korean Peninsula. Specifically, we should abandon our “One Korea” policy, long embraced by Republicans and Democrats. It’s no longer realistic or viable.
North Korea has reopened a hotline to South Korea, almost two years after it was disabled on the orders of leader Kim Jong-un,
South Korea confirmed it had received a call from the North at 15:30 local time (06:30 GMT) on Wednesday.
The North Korean leader had earlier said he was open to dialogue with Seoul and to sending a team to the Winter Olympics in the South next month.
The two nations have not held high-level talks since December 2015.
North Korea cut off the communications channel shortly afterwards, refusing to answer calls, according to officials in the South.
A North Korean official announced the hotline's re-opening in a televised statement.
He said the two nations would discuss the practical issues around a proposal to send a North Korean delegation to the Winter Games in Pyeongchang in February.
"We will make close contact with South Korea in a sincere and faithful manner," Yonhap news agency quoted the official as saying. He said the countries would "discuss working-level issues" about sending the delegation.
North Korea is to send a delegation to the 2018 Winter Olympic Games taking place in South Korea in February, officials from the South say.
The breakthrough announcement came as the countries met for their first high-level talks in more than two years.
The delegation will include athletes, officials and supporters.
South Korea also proposed holding family reunions during the Winter Olympics for people separated by the Korean War.
What's happened at the talks?
They have resumed after a break for lunch and the developments have been conveyed by officials from the South:
Vice unification minister Chun Hae-Sung told journalists: "The North side proposed dispatching a high-level delegation, National Olympic Committee delegation, athletes, supporters, art performers, observers, a taekwondo demonstration team and journalists" to the Games.
The South proposed that athletes from both Koreas march together at the opening ceremony in Pyeongchang as they did at the 2006 Winter Olympics
The South pushed for family reunions, a highly emotional issue for both countries, to take place during the Lunar New Year holiday, which falls in the middle the Games.
The South also proposed resuming negotiations over military issues and the North's nuclear programme.
The South said it would consider temporarily lifting sanctions, in co-ordination with the UN, to facilitate the North's participation in the Olympics.
The North's response to all of the South's proposals is not yet known. The opening remarks of head of the North Korean delegation, Ri Son-gwon, were fairly neutral.
He said he hoped the talks would bring a "good gift" for the new year and that the North had a "serious and sincere stance".
Where are the talks and how did they come about?
The talks began early on Tuesday in the Panmunjom "peace village" in the demilitarised zone (DMZ) at the border.
There are five senior officials on each side.
In his New Year address, North Korean leader Kim Jong-un had said he was considering sending a team to the Olympics. South Korea's Olympics chief had said last year that the North's athletes would be welcome.
Following Mr Kim's overture, the South then proposed high-level talks to discuss the North's participation, but the North only agreed to the talks after the US and South Korea agreed to delay their joint military exercises until after the Olympics. The North sees the annual drills as a rehearsal for war.
Some critics in the US see the North's move as an attempt to divide the US-South Korea alliance.
Analysis: BBC's Rupert Wingfield-Hayes in Seoul
A little over a week ago North Korea was threatening nuclear war - this morning a delegation from Pyongyang strode across the demarcation line that divides North and South Korea and agreed a North Korean delegation would attend the Pyeongchang Games.
It is a sudden and dramatic change after months of tension. But few in the South believe any of this demonstrates a fundamental shift in Pyongyang's position.
Experts say North Korea's leader Kim Jong-un has become increasingly fearful that the US is planning a military strike against him, and has decided he must do something to de-escalate tensions.
South Korea's president Moon Jae-in has been thrust in the delicate position of trying to engage the North in genuine dialogue, while not upsetting his very sceptical American ally.
When were the last talks?
Back in 2015.
Relations then broke down after Seoul suspended a joint economic project at the Kaesong Industrial complex in North Korea following a rocket launch and nuclear test by the North.
The incident led to North Korea ending all communication with Seoul, including cutting off telephone lines.
Tensions have risen in the years since, as the North continues to rapidly advance its banned nuclear weapons programme.
What might we expect at the Olympics?
Pyeongchang, approximately 180km (110 miles) east of Seoul, will host both the Winter Olympics in February and the Winter Paralympics in March.
There has been no official announcement on the make-up of the North Korean team.
Only two North Korean athletes had qualified for the Games - figure skaters Ryom Tae-ok and Kim Ju-sik - although even they missed the participation deadline and would need IOC clearance.
There may be possible wild-card entries, perhaps in short-track speed skating and Nordic skiing, but this has not been confirmed.
North Korea has participated in the Olympics before, but not in South Korea. It boycotted the 1988 Olympic Games in Seoul.
After the Korean war ended in a truce in 1953, Panmunjom was designated as the one place where officials from both sides could meet.
The "truce village" is divided into two parts by a military demarcation line: one side belonging to the North, the other to the South.
In the middle of the village sit the UN Command buildings, crossing the middle of the line.
Last year, a North Korean defector made a dash through the DMZ, managing to cross over to the South Korean side of Panmunjom.
North and South Korea have agreed to march together under a single "unified Korea" flag at next month's Winter Olympics in the South.
They also agreed to field a joint women's ice hockey team in rare talks at the truce village of Panmunjom.
These are the first high-level talks between the two Koreas in more than two years.
The Games will take place between 9 and 25 February in Pyeongchang in South Korea.
If the plans are realised, a hundreds-strong North Korean delegation - including 230 cheerleaders, 140 orchestral musicians and 30 taekwondo athletes - could cross into the South via the land border to attend.
The North has also agreed to send a smaller, 150-member delegation to the Paralympics in March.
Both South Korea's hockey coach and conservative newspapers had expressed concern about the prospect of a united hockey team, saying it could damage South Korea's chances of winning a medal.
Tens of thousands of people are said to have signed online petitions urging President Moon Jae-in to scrap the plan.
And it will have to be approved by the International Olympic Committee (IOC) meeting in Lausanne, Switzerland, on Saturday, because North Korea has missed registration deadlines or failed to qualify.
A new mobile phone app developed in North Korea allows its users to experiment with new looks.
While such photo manipulation apps are common around the world, it appears that Bomhyanggi 1.0 (Spring Scent) is the first of its kind for smartphone users in the Communist country.
According to North Korean news outlet DPRK Today, the Spring Scent app helps its users "explore what type of makeup techniques would be the best for themselves by trying different types of makeup tools virtually".
It has, developers Kyeonghung Information Technology Store say, "gained very positive feedback from women in North Korea".
North Korea has two official mobile phone networks, but contacting the world beyond its borders by phone or through the global internet is technically impossible.
Instead, there is a growing internal market in mobile phone applications for news, information and entertainment, many resembling products available worldwide.
Among them is Soccer Fierce Battle, a 3D football simulation compatible with PCs and mobile devices operating the Android system.
The game closely resembles the best-selling FIFA video game series, Seoul's Korea Herald newspaper reported last August.
Another popular game is Hunting Yankee, a shoot-em-up in which American soldiers are the enemy, the South China Morning Post says.
North Korea makes its own tablet computers and mobile phones running a domestically-produced version of the Android operating system, and there are more than 3.5m users in the country, Japan's Nikkei reported last month.
According to the New York Times, Pyongyang reportedly imports mobile phones and electronics from Chinese companies, exploiting a loophole in sanctions on luxury goods that leaves exporting countries to define what exactly these goods might be.
"You will get to see yourself becoming more beautiful," the app's promotional material boasts.
A recent report in the Seoul-based Daily NK claims that there's a growing interest in skin care and beauty north of the border, thanks to highly illegal interest in South Korean television dramas smuggled into the country.