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.
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.
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,” Andrea says 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.
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 andnobody 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.