The official, who is well-versed in North Korea affairs, spoke as there is growing alarm about the North's saber-rattling. On July 4, Pyongyang successfully tested an intercontinental ballistic missile capable of reaching Alaska and Hawaii.

"We're now at a point where this is going to become a fait accompli pretty soon," he said on the condition of anonymity.

"Whenever we think, 'What are we going to do?' we have to think, 'How is he going to respond? What activities are we going to prompt in him? What conditions are we going to create for (North Korean leader) Kim Jong-un?'"

The Donald Trump administration has repeatedly warned that the US could use military options in response to the North's mounting threats. Pyongyang claims its missile and nuclear program is aimed at deterring what it calls US hostility.

"The fact that he's absolutely committed to the nuclear program, it's the same as the father," the official said, referring to Kim and his late father and former leader, Kim Jong-il. "It's just now, it's near culmination."

 The official also pointed to a different pattern of provocations and responses under Kim. During the rule of his grandfather and North Korea founder Kim Il-sung, there was a 10-year cycle of provocations, negotiations with the US and subsequent concessions. That was shortened to five years under his son, and then to a year at most under his grandson, according to the official.

"I think you can absorb those cycles with a 10-year or five-year (period). One year cycle -- this is going to create conditions that drive us toward a response that doesn't exist inside that current cycle," he said.

Asked if chances are higher now for a military response, he noted, "The fact that they're more frequent provocation cycles doesn't necessarily make them (military options) more likely because it really is the degree of provocation."

In different political conditions, the North's sinking of a South Korean warship in 2010 could have prompted a military response, he added.

The official also underscored the threat posed by North Korea's conventional military capabilities, including its army, the fourth largest in the world. (Yonhap)