North Korean leader says will only use nuclear weapons if attacked

Pyongyang: North Korean leader Kim Jong-Un told a rare ruling party congress that his country was a "responsible" nuclear weapons state, with a no first-use policy and a commitment to non-proliferation, state media reported on Sunday.

Speaking to thousands of delegates gathered for the first Workers' Party congress in more than 35 years, Kim also announced a new five-year plan to boost the impoverished country's moribund economy and "revitalise" people's lifestyles.

His remarks yesterday, the second day of the congress, came amid growing concerns that the North might be on the verge of conducting a fifth nuclear test.

Kim had opened the congress with a defiant defence of the nuclear weapons programme, praising the "magnificent... And thrilling" test of what Pyongyang claimed was a powerful hydrogen bomb on January 6.

But his report to the conclave yesterday stressed that North Korea was also a "responsible nuclear weapons state" with an arsenal built for deterrence.

"Our republic will not use a nuclear weapon unless its sovereignty is encroached upon by any aggressive hostile forces with nukes," he said, according to an English translation of his speech by the North's official KCNA news agency.

That formula would appear to allow for the use of nuclear weapons against a conventional attack by a nuclear power, but the Korean-language version made it clear that the scenario involved an actual nuclear attack.

Kim also vowed that Pyongyang would "faithfully fulfil" its non-proliferation obligations and push for global denuclearisation.

North Korea withdrew from the global Non-proliferation Treaty (NPT) in 2003 - the first signatory country to ever do so.

Pyongyang's nuclear weapons doctrine has always been a complex mix of self-defence, deterrence and threat.

At the time of its first nuclear test in 2006, North Korea stressed that it would "never use nuclear weapons first".

And when it codified its nuclear programme in North Korea law in April 2013, it stated that nuclear weapons could only be used to repel invasion or attack by another nuclear power.

But in recent years, and especially in the wake of tough UN sanctions imposed over its fourth test in January, it has issued repeated warnings of pre-emptive nuclear strikes against South Korea and the United States.

"The survival of the ruling Kim family is intimately linked to nuclear arms because they help legitimise Kim Jong-Un's hereditary rule and keep his foreign foes at bay," said Alexandre Mansourov, an expert on North Korean security issues.

The party congress is widely seen as Kim's formal "coronation" as supreme leader, more than four years after he took power following the death of his father, late ruler Kim Jong-Il, in December 2011.