North Korea’s ability to use nuclear weapons is increasing ‘with each passing month’, according to a former US State Department negotiator.

Robert Gallucci, previously US special envoy on North Korea’s nuclear weapons programme, said the current American approach towards North Korea was not working.

Mr Gallucci led the 1994 negotiations with the North Korean government that led to a nuclear freeze deal.

Speaking during a seminar at John Hopkins University in Washington, he said: “We could continue just as we are now. We could continue with what might be called some version of containment, where we have a sanctions regime we attempt to limit the North Korean options politically and economically.

“But...as we do contain the North, we also watch the situation get worse.

“The North Korean case is not like fine wine. It doesn‘t get better with age. With each passing month and year, we look at a nuclear weapons capability that grows qualitatively and quantitatively.

Mr Gallucci suggested the next US president should prioritise negotiations with North Korea, but said they should not offer concessions such as the end of joint military exercises with South Korea – something Pyongyang has long called for.

And he called on the US government to stop "sub-contracting" resolution of the issue to China.

He said: "We want the Chinese to move the North to the proper frame of mind and enter negotiations. But we should not subcontract this issue, the North Korea issue, to Beijing.

“So I say, cooperate with the Chinese, get them to do as much as possible, but don't expect them to do the whole job.”

North Korea would be willing to surrender its nuclear weapons if an agreement guarantees the regime’s “survival with as much certainty as they think nuclear weapons will give them as deterrent to U.S efforts at regime change”, Mr Gallucci added.

It comes as satellite images suggest the authoritarian state could be gearing up for another nuclear weapons test.

US-based monitoring group 38 North said satellites had recorded on-going activity at Punggye-ri - North Korea’s main nuclear test site.

The country’s fifth and most recent nuclear test took place on 9th September, leading it to announce it had successfully detonated a nuclear warhead that could be mounted onto a ballistic missile.

The test caused the UN Security Council to “strongly condemn” North Korea while US President Barack Obama warned the country will face “consequences to its unlawful and dangerous actions”.