US President Donald Trump has said he would like to solve the North Korea crisis diplomatically, but that a "major, major conflict" is possible.
China's foreign minister called for negotiation and dialogue.
The UN Security Council is meeting to discuss North Korea on Friday and will consider further measures to counter its nuclear and missile programmes.
The country has made several military shows of strength in recent weeks but a missile it was testing failed.
America sent warships to the region and began installing a controversial anti-missile system in South Korea earlier this week.
US Secretary of State Rex Tillerson said Washington would negotiate with North Korea with a view to removing nuclear weapons from the country, not changing the government.
He told NPR radio in the US: "We do not seek regime change, we do not seek a collapse of the regime, we do not seek an accelerated reunification of the peninsula.
"We seek a denuclearised Korean peninsula - and that is entirely consistent with the objectives of others in the region as well."
North Korea has carried out repeated missile tests in recent months and is threatening to conduct its sixth nuclear test.
Mr Tillerson also indicated that he thought China, North Korea's major ally, might be starting to see the regime as a "liability" or a security risk.
"What China is beginning to re-evaluate is whether North Korea is any kind of an asset to them, or whether North Korea themselves and the regime have become a liability to China's own security," he said.
Shortly after being elected, Mr Trump accused China of not doing enough to rein in North Korea and suggested the US could take unilateral action.
But Chinese Foreign Minister Wang Yi has warned that tensions on the Korean peninsula risk getting out of control, and ahead of Friday's meeting he said negotiations with North Korea are "the only right choice".
According to Mr Tillerson, China has told the US it will impose sanctions on North Korea if it conducts further nuclear tests.
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In a wide-ranging interview inside the Oval Office, Mr Trump praised China's President Xi Jinping for his handling of North Korea, calling him "a very good man" who loved his country.
He said Mr Xi "certainly doesn't want to see turmoil and death".
"He is a very good man and I got to know him very well," he said.
"He loves China and he loves the people of China. I know he would like to be able to do something, perhaps it's possible that he can't."
Mr Trump also said it had been "very hard" for Kim Jong-un to take over North Korea at such a young age.
He said: "He's 27 years old. His father dies, took over a regime. So say what you want but that is not easy, especially at that age."
But he stressed he was "not giving him credit", and added: "I hope he's rational."
"There is a chance that we could end up having a major, major conflict with North Korea. Absolutely," said Mr Trump.
Other developments have raised tensions in recent weeks:
- North Korea executed a failed missile launch and held a massive military parade in an apparent show of strength
- The US deployed a group of warships and a submarine to the region
- Pyongyang reacted angrily, threatening a "super-mighty pre-emptive strike"
- The US began installing a controversial $1bn (£775m) anti-missile system system called Thaad in South Korea - which Mr Trump said South Korea should pay for. Seoul said on Friday there was "no change" in its position that the US pays for it
- Mr Tillerson and US Vice President Mike Pence visited South Korea, reiterating that "all options are on the table" in dealing with the North
In February, China banned coal imports from North Korea - one of the country's key exports - and is reportedly also considering restricting oil shipments if Pyongyang continues to behave belligerently.
What else did Mr Trump say?
The president reflected on how the demands of his job were greater than his "previous life", which he said he had loved.
"You're really into your own little cocoon, because you have such massive protection that you really can't go anywhere," he said.
"I like to drive. I can't drive any more."
On other key topics, Mr Trump said:
- He would speak to Mr Xi before again contacting Taiwan's president, Tsai Ing-wen, after China lodged a formal complaint over a phone call he made in December
- He said so-called Islamic State must be eradicated and that Islamist extremism had to be defeated - "and it has to be humiliation"
- He could see no reason why Israel and the Palestinians should not make peace
Earlier, Russia's President Vladimir Putin called for the resumption of talks with North Korea.
Speaking in Moscow, where he met Japanese Prime Minister Shinzo Abe, he urged those involved to "refrain from using belligerent rhetoric".