The concession was made just days before crunch talks with South Korea and weeks before Kim and the US President meet in a crucial summit.
All six of North Korea‘s underground nuclear tests were carried out at the Pyunggye-ri test site, including the last and largest in September.
The pledge to halt the nuclear weapons programme initiated by his grandfather, Kim Il-sung, is a significant U-turn by the 34-yearold leader, who has made the security of North Korea his main policy since acceding to power in 2011.
International sanctions are known to be biting, particularly since last year when they were supported by his main ally, China, and are hampering Kim’s aim of military and economic development.
Humanitarian agencies can no longer operate north of the 38th parallel and Beijing’s decision not to import North Korean textiles has starved Pyongyang of a vital source of currency. China also stopped the export of petroleum, the lifeblood of North Korea’s military.
Donald Trump’s threat of military action carried more weight in the face of fuel shortages in the armed forces, former Japanese intelligence chief Sakai Takahashi said.
“Sanctions on their own are ineffective against a regime which is too used to the hardship of its people,” he said.
South Korean expert and journalist Sukha Kwon said: “North Korea may have a two-million man army but its equipment is old. We know that Kim was struggling even to hold military exercises because of the fuel implications. Kim is all too aware that his forces would last two or maybe three days in the event of a full conventional attack.
“Takahashi is clear the military threat was the final deciding factor and, while South Korea’s President Moon receives credit for inviting North Korea to the Winter Olympics, it is a view shared by most people in South Korea.”
The decision to announce the freeze well before the summit came after Kim convened a meeting of the Central Committee of the ruling Workers’ Party on Friday and was hailed by experts as a sign of his sincerity.
But others urged caution. “What Kim has actually done is to confirm he has developed his nuclear forces sufficiently and can afford to freeze the programme now,” said James Hoare, ex-British charge d’affaires in Pyongyang.
“I doubt that will be enough for the US who, like Japan, will want guarantees of total denuclearisation. “We’ve been here before and it didn’t take North Korea long to get back on the nuclear track after it abandoned the agreed framework in 2002.”
Sukha Kwon said: “President Moon’s young supporters are very optimistic but the rest of the country is suspicious Kim is playing for time to build up his economy. Even if he dismantles his entire nuclear programme, he will retain the expertise and materials to build it up again.”
Mr Trump, who will come to Britain for a state visit this summer, said the decision to suspend nuclear tests was good news for North Korea and the world.