The former Pyongyang diplomat believes the despotic tyrant “will press the button” if he feels his rule is under threat.
His comments come as Kim accelerates North Korea’s production of weapons-grade plutonium and its ballistic missile capabilities.
Following the collapse of an international non-proliferation agreement, the dictator has amassed 50kg of plutonium after reactivating a nuclear power plant in 2013, according to a report from South Korea's defence ministry.
Thae Yong-ho warned Kim Jong-un would be willing to launch a nuclear attack on the US
Kim Jong-Un, I think, will press the button of this dangerous weapon
Former North Korean diplomat to London, Thae Yong-ho, fled the brutal regime to the South in August 2016.
He was one of the highest-ranking officials ever to defect from the secretive nation, where much of life still remains shrouded in mystery.
Thae Yong-ho made the chilling warning during an interview with the BBC's Steve Evans
“Kim Jong-un knows quite well that nuclear weapons are the only guarantee for his rule,” Mr Yong-ho said.
“Kim Jong-un, I think, will press the button of this dangerous weapon when he thinks that his rule and his tenacity is threatened.”
He said he believed North Korea would launch the attack, even if the potential retaliatory military action would likely result in the collapse of Kim's rule.
“He knows that if he loses the power then it is his last day so he may do anything, even to attack Los Angeles," Mr Yong-h added. "Because once people know that in any way you will be killed, then you will do anything. That is the human being's normal reaction".
America and South Korea prepare for war against North Korea
Tue, January 24, 2017
U.S. and South Korean marines participate in the endurance exercise in temperature below minus 20 degrees celsius under a scenario to defend the country from any possible attacks from North Korea.
1 of 18
Although North Korea does not have the arsenal to strike the US, combative messages out of Pyongyang have warned it is getting ever closer.
During his New Year address, Kim boasted the country was in its “final stages” of test-firing a fully fledged intercontinental ballistic missile.
The missile has a range of 5,500 miles could cause world-wide devastation if its unhinged leader decided to launch an attack.
"Research and development of the cutting-edge tech weapons are actively progressing and strengthening our defence capabilities, including last stage preparation of tests for intercontinental ballistic rocket launch have been continuously succeeding," he said on state television.