President Donald Trump on Sunday said that North Korean leader Kim Jong-un is a "smart cookie," but insisted that military options remains on the table in the face of continuing provocations from Pyongyang.

"At a very young age, he was able to assume power. A lot of people, I'm sure, tried to take that power away, whether it was his uncle or anybody else. And he was able to do it. So obviously, he's a pretty smart cookie," Trump said in an interview with "Face the Nation" that aired Sunday on CBS.

"But we have a situation that we just cannot let - we cannot let what's been going on for a long period of years continue," he added.

Regarding the ballistic missile tests by the North Korean regime, the president said that he is working with Chinese President Xi Jinping, one of the few leaders to whom Pyongyang listens, to reduce tensions and try to pressure Kim to negotiate an end to his nuclear program.

"If he does a nuclear test, I will not be happy. And I can tell you also, I don't believe that the president of China, who is a very respected man, will be happy either," said Trump, who this weekend hit the 100-day mark in office.

When asked if a new nuclear test by Pyongyang would lead to US military action, Trump said: "I don't know. I mean, we'll see."

"People are saying: 'Is he sane?' I have no idea ... but he was a young man of 26 or 27 ... when his father died. He's dealing with obviously very tough people, in particular the generals and others," said Trump when asked for his take on the North Korean leader.

Pyongyang on Saturday staged a new ballistic missile test, but the projectile apparently exploded just minutes after being launched, according to South Korean and US military sources.

Washington has asked China for help in getting North Korea back to the negotiation table but has not ruled out military action to prevent Pyongyang from developing a nuclear missile that can hit the US if diplomacy does not work.