How potent are North Korea's threats?
Since the latest UN sanctions, North Korea has unleashed a salvo of threats against the US and South Korea, even vowing to restart operations at its main nuclear complex. The BBC examines how much of a threat North Korea really poses to the US and its Asian neighbours.
North Korea's threats
North Korea has frequently employed bellicose rhetoric towards its perceived aggressors.
The 1994 threat by a North Korean negotiator to turn Seoul into "a sea of fire" prompted South Koreans to stock up on essentials in panic.
End Quote Professor John Delury, Yonsei university
When you look at occasions where something really did happen, such as the artillery attack on a South Korean island in 2010, you see there were very clear warnings”
After US President George W Bush labelled it part of the "axis of evil" in 2002, Pyongyang said it would "mercilessly wipe out the aggressors".
Last June the army warned that artillery was aimed at seven South Korean media groups and threatened a "merciless sacred war".
There is also a pattern of escalating threats whenever South Korea gets a new leader.
While many observers dismiss the rhetoric as bluster, others warn of "the tyranny of low expectations" when it comes to understanding North Korea, because there have been a number of serious regional confrontations.
"If you follow North Korean media you constantly see bellicose language directed against the US and South Korea and occasionally Japan is thrown in there, and it's hard to know what to take seriously. But then when you look at occasions where something really did happen, such as the artillery attack on a South Korean island in 2010, you see there were very clear warnings," Professor John Delury at South Korea's Yonsei university told the BBC.
The North consistently warned that military exercises being conducted in the area would spark a retaliation.
Mr Delury argues that misreading Pyongyang's intentions and misunderstanding its capabilities has kept the US and South Korea stuck in a North Korean quagmire.
Picking apart the bluster
The latest warning of a pre-emptive nuclear attack was in response to joint military exercises between South Korea and the US rather than sanctions per se.
"Any time a nation threatens pre-emptive nuclear war, there is cause for concern. North Korea is no exception, with its recent shift in rhetoric from accusing the US of imagining a North Korean ballistic missile threat, to vowing to use its ballistic missile capabilities to strike the continental US," says Andrea Berger, from the Royal United Services Institute in London.
But many experts believe these threats come from the North's desire for a peace treaty with the US.
"It seems to believe that it will not be taken seriously until it can enter talks on this issue with sizeable military strength. This is in line with Pyongyang's historic military-first policy," Ms Berger says.
The US is often centre-stage. "There are cases where the threats are geared towards getting on the radar particularly of the White House, which tries to ignore North Korea as a matter of policy. Pyongyang's message is - you cannot break us, we will not go away, you have to deal with us," Mr Delury said.
The latest series of threats are being seen as "bluff" because the North's leaders know a nuclear attack would be suicidal and impractical, given the North's rudimentary missile programme.
And many point out that it is unclear exactly which pacts North Korea has abandoned as some were never properly implemented. And the North has also threatened to scrap the armistice agreement before this - there are several well documented attempts.
But the North may yet respond to sanctions by provoking a conventional forces border clash with South Korea, either on land or sea, as it has done before.
It has now said it will restart operations at its main nuclear facility at Yongbyon - this could open up a new source of plutonium for the North's weapons programme.
When it comes to enriching uranium, it is unclear how many secret plants already exist and there is still no clear evidence to indicate whether the North's latest nuclear test was uranium-based. Nevertheless, experts say facilities at Yongbyon could be converted to produce weapons-grade uranium.
Is the US a real target?
South Korean tests carried out on fragments of a rocket fired in December in what the North describes as a satellite launch showed it would have had a range of more than 10,000km (6,200 miles), putting the US well within striking distance.
However, there is little evidence that North Korea has yet developed a guidance system to ensure an accurate strike, or the re-entry technology to bring an intercontinental ballistic missile (IBM) back down.
Pyongyang's ability to carry out a nuclear strike on the US is even less certain, as analysts do not believe it has yet managed to create a small enough nuclear device to be mounted on a warhead.
December's missile launch, the International Institute for Strategic Studies said, proved that North Korea has something that can hit American shores but it says that any "functioning nuclear-tipped intercontinental ballistic missile is still at least several years away".
North Korea has shown it is determined to pursue this technology. Its latest underground nuclear test was double the size of the previous one in 2009.
The North claimed that a nuclear test in February detonated "an atomic warhead that is lighter and miniaturised but with a big explosive charge".
But while the North might struggle to hit the US, it could target US interests in the region. There are more than 28,000 US military personnel based in South Korea, another 40,000 in Japan and a large military base in Guam, a US territory off the Philippines.
The US is also obliged to defend Japan if it is attacked under the terms of the post-World War II security alliance between Washington and Tokyo.
Even if a missile is launched from the North, Washington has insisted it is "fully capable" of blocking any attack against it or its allies.
It is also worth noting that the only US Navy ship being held by a foreign power is in Pyongyang.
The USS Pueblo was captured while on a surveillance mission in 1968. It was in international waters during its mission and nobody imagined that the North Koreans might capture it - so the crew were unprepared.
One crew member died and 82 were taken to North Korean prison camps, where they were held for 11 months, accused of spying. They were released once the US apologised and insisted the ship had not been spying - later retracting both statements.
North Korea's neighbours
The Cheonan sank close to the disputed sea boundary between North and South Korean territorial waters, along which the two navies have clashed a number of times in the past decade”
Since the Korean War ended, Pyongyang has repeatedly shown its ability to strike neighbours and foreign interests in the region, often in response to what it sees a provocation.
In 1967, it attacked and sank South Korea's vessel the Dangpo as it patrolled in the Yellow Sea, killing 39 of the crew.
There followed a period of relative calm - though sabre-rattling continued - as South Korea pursued its "Sunshine Policy", an attempt to steadily build closer relations and reduce tensions between 1998 and 2008.
But in March 2010, the South Korean warship Cheonan travelling close to the disputed maritime border - known as the Northern Limit Line (NLL) - was split in half by an explosion, leaving 46 sailors dead. South Korea said the only "plausible explanation" was that it had been hit by a North Korean torpedo. Pyongyang denied this.
In November that year, North Korean troops launched an artillery strike on South Korea's Yeonpyeong Island, just south of the NLL. Two South Korean marines and two civilians were killed. Pyongyang said the clash was provoked by a South Korean military drill being conducted near the island.
North Korea has a conventional army of more than 1.1m, but its equipment is thought to be Soviet-era and in poor condition.
However it still has a vast amount of artillery lined up along the demilitarised zone, and the South Korean capital Seoul is within its reach.
According to the International Institute for Strategic Studies' military balance, approximately 65% of North Korea's military units, and up to 80% of its estimated aggregate firepower are within 100km of the DMZ.