ⓒYONHAP News

"He definitely likes sending rockets up, doesn't he? That's why I call him rocket man."

"We have a very good relationship and we'll see what happens. It may work or not... "

The "rocket man" nickname was invoked again during a 50-minute question and answer session on the sidelines of a NATO summit in London Tuesday.

Asked why nuclear negotiations aren't moving forward, U.S President Donald Trump also outlined a worst case scenario with North Korea.

"If you would’ve listened to President Obama, we’d be in a World War Three right now. So we’ll see what happens... "

"Now we have the most powerful military we’ve ever had and we’re by far the most powerful country in the world. And, hopefully, we don’t have to use it, but if we do, we’ll use it. If we have to, we’ll do it."

He then pressed the young North Korean leader to abide by the agreements reached during their summit in Singapore last year.

"You know my relationship with Kim Jong-un is really good but that doesn't mean he won't abide by the agreement we signed. You have to understand, you have to go look at the first agreement that we signed. It said he will denuclearize. That's what it said. I hope he lives up to the agreement but we're going to find out."

The comments came as the U.S. is increasing its surveillance of North Korea, flying P-3C and other reconnaissance aircraft over the Korean Peninsula.

Following the collapse of his second meeting with Trump in Hanoi in February, North Korean leader Kim Jong-un set a year-end deadline for the Trump administration to find a breakthrough in stalled nuclear talks.

With that deadline fast approaching, the Kim regime has begun to insinuate that its nuclear and intercontinental ballistic missile activities might resume as Trump’s foreign policy remains a work in progress.