US President Donald Trump has described North Korean leader Kim Jong-un as a "pretty smart cookie".
Speaking to CBS, he noted Mr Kim had assumed power at a young age, despite dealing with "some very tough people".
Amid escalating tensions over North Korea's nuclear programme, he said he had "no idea" whether Mr Kim was sane.
The North Korean leader had his uncle executed two years after he came to power, and is suspected of ordering the recent killing of his half-brother.
President Trump, asked what he made of the North Korean leader, answered:
"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.
"And 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."
The interview on the Face the Nation show came after North Korea's second failed ballistic missile test in two weeks, in which a missile exploded shortly after it was launched on Saturday.
When asked why the missiles "keep blowing up", Mr Trump said: "I'd rather not discuss it."
"We shouldn't be announcing all our moves," he said. "It is a chess game. I just don't want people to know what my thinking is."
North Korea is believed to be continuing efforts to miniaturise nuclear warheads and fit them on long-range missiles capable of reaching the US.
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Tensions in the region have increased lately, with both North and South Korea conducting military exercises.
America sent warships to the region and began installing a controversial anti-missile system in South Korea earlier this week.
On Sunday, an article from Pyongyang's state-run news agency KCNA urged the US to "ponder over the catastrophic consequences to be entailed by their foolish military provocation".
North Korea has carried out repeated missile tests in recent months and is threatening to conduct its sixth nuclear test.
President Trump said the US was "not going to be very happy" if further tests were carried out. When asked whether this would mean military action he said: "I don't know. I mean, we'll see."
Mr Trump said the Chinese President Xi Jinping, an ally of North Korea, was "putting pressure" on Mr Kim to scale back his nuclear and military activities.
"But so far, perhaps nothing's happened and perhaps it has," he said.
He again hailed the ties he has been developing with China, a country he criticised heavily during his election campaign.
"The relationship I have with China, it's been already acclaimed as being something very special, something very different than we've ever had," Mr Trump said.
When asked whether he would fulfil his campaign pledge to label China a currency manipulator, he said "as soon as I got elected, they stopped", but implied he did not want to jeopardise Chinese co-operation on North Korea.
"North Korea is maybe more important than trade. Trade is very important. But massive warfare with millions, potentially millions of people being killed? That, as we would say, trumps trade."
Also in the interview:
- On the healthcare bill he is negotiating, he said pre-existing conditions would be fully covered and premiums would be lower.
- On alleged Russian election hacking: "I'll go along with Russia. Could've been China, could've been a lot of different groups."
- On releasing his tax return, he said he would make a decision when the current audit was complete, adding: "I have a very big tax return."
- On making legislation: "The rules in Congress and in particular the rules in the Senate are unbelievably archaic and slow moving. And in many cases, unfair. In many cases, you're forced to make deals that are not the deal you'd make."
- On being president: "It's something that I really love and I think I've done a very good job at it... It's a tough job. But I've had a lot of tough jobs. I've had things that were tougher."