“Once he sees that there is any kind of sign of a tank or an imminent threat from America, then he would use his nuclear weapons with ICBM,” he added in an exclusive interview on Sunday.

Thae was living in London and serving as North Korea’s deputy ambassador to the United Kingdom when he and his family defected to South Korea and were announced to the world in August.

He was not directly involved in North Korea’s weapons program but believes his country “has reached a very significant level of nuclear development.”

North Korea is estimated to have upward of eight nuclear weapons but has not demonstrated the ability to attach them to a long-range rocket, an ICBM, capable of hitting the U.S.