North Korea's shrill threats of nuclear war may seem overblown or absurd, but they are well tailored to a domestic audience raised on the constant fear of imminent US invasion, analysts say.

While Pyongyang's warlike rhetoric has to reach a certain decibel-level for the rest of the world to take note, North Koreans are weaned on a relentless, daily propaganda formula almost from birth.

It paints a reality of North Korea as a racially pure nation surrounded by scheming enemies -- led by the United States -- who are bent on invasion and enslavement.

Problems like food shortages are the fault of unfair, punitive sanctions aimed at weakening the North which must therefore focus all its resources on national defence for a final, decisive battle that could come at any time.

From that viewpoint, the blistering threats and warnings emanating from Pyongyang make perfect sense, and the clearly exaggerated claims for the North's nuclear strike capability are -- in the absence of any information to the contrary -- taken at face value.

"The guy in the White House National Security Council knows it's absurd, but the guy watching on TV in Pyongyang is probably roaring his country on," said Daniel Pinkston, a North Korea analyst with International Crisis Group.

B.R. Myers, an expert in North Korean propaganda, believes Pyongyang is exploiting current tensions to incite workers and get them to channel their rage at the US into projects such as a land-reclamation drive on the east coast.

"The regime can no longer fire up people with any coherent or credible vision of a socialist future, so it tries to cast the entire workforce... as an adjunct to the military," he told the New York Times.

"Work places are 'battlegrounds', and all labour strengthens the country for the final victory of unification," said Myers, professor of international studies at Dongseo University in Busan, South Korea.

Defectors note that much of working life in North Korea is placed in a combative, martial context.

"We were at war all the time, all year round," Oh Ji-Heon, who fled the North in 2010, told the defector-run website, New Focus International.

"In spring, there was the 'war of rice planting'. In summer the 'war of weeding'. Autumn was the 'harvest war' and in winter we fought the 'fishing war'," Oh said.

"Every season brought a new enemy for us to conquer," she added.

The constant reinforcement of this state of permanent warfare means that inside North Korea at least, there is far less of a disconnect between people's daily lives and the regime's apocalyptic rantings against Washington and Seoul.

The outside world may roll its eyes at choreographed outpourings of public joy, grief or anger shown on television, but the fact they are stage-managed does not necessarily mean they misrepresent public passions.

Orchestrated displays traditionally gear up around the time of key dates, such as the annual April 15 celebrations of late founder Kim Il-Sung's birthday.

The regime makes strenuous efforts to raise nationalist emotions to their peak for such events which provide a key opportunity to hammer home the message of a brave, encircled country united against a common foe.

"The bottom line is that the average North Korean more or less believes the government version of reality," said long-time North Korea watcher Andrei Lankov, a professor at Kookmin University in Seoul.

"Even those who might be quite sceptical have enormous pride in their country and believe themselves to be the victims of a US conspiracy and under imminent threat of attack," Lankov said.

To maintain this siege mentality, which it can exploit in numerous ways, the North Korean elite not only relies on a pervasive propaganda programme, but also a tight national information cordon.

Although new technology -- smuggled mobile phones and MP3 players -- have allowed more outside news to creep in, North Koreans still live in the most censored, isolated society on the planet.

"It's easy to read North Korean propaganda, especially when it's at these current levels, as proof of mass national paranoia," Lankov said.

"North Koreans aren't paranoid or delusional. They just don't have access to a reality that would challenge the assumptions they are fed," he said.

The North's rhetoric has climbed to new heights recently with fresh threats of "thermo-nuclear" war and warnings to foreigners living in South Korea that they should consider leaving for their own safety.

But there are signs that the general atmosphere inside the country has shifted with the end of reservist military exercises.

Sources in the North cited by the defector-run Internet newspaper Daily NK said that, up until last month, there were worker and farmer reservists on the streets, all armed and in uniform.

"Now there are only workers with shovels, mobilized to produce manure for the farms. Even those soldiers who were living underground in the mountains have returned to barracks," said one source.