The US has urged all nations to cut diplomatic and trade ties with North Korea after the country's latest ballistic missile test.
Speaking at the UN Security Council, US envoy Nikki Haley said President Trump had asked his Chinese counterpart to cut off oil supplies to Pyongyang.
She said the US did not seek conflict but that North Korea's regime would be "utterly destroyed" if war broke out.
The warning came after Pyongyang tested its first missile in two months.
North Korea said the missile fired on Wednesday, which it said reached an altitude of about 4,475km (2,780 miles) - more than 10 times the height of the International Space Station - carried a warhead capable of re-entering the Earth's atmosphere.
The claim was not proven and experts have cast doubt on the country's ability to master such technology.
However, North Korea's leader Kim Jong-un called the launch "impeccable" and a "breakthrough".
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The test - one of several this year - has been condemned by the international community and the UN Security Council called an emergency meeting.
Ms Haley warned that "continued acts of aggression" were only serving to further destabilise the region.
Russia's UN ambassador Vassily Nebenzia said North Korea should stop its missile and nuclear tests but also called on Washington to cancel military exercises with South Korea planned for December as it would "inflame an already explosive situation".
China also suggested the North should stop the tests in return for a halt to US military exercises - a proposal Washington has rejected in the past.
Cutting the oil lifeline
"We need China to do more," Ms Haley said on Wednesday. "President Trump called President Xi this morning and told him that we've come to the point where China must cut off the oil for North Korea.
"We know the main driver of its nuclear production is oil," she said. "The major supplier of that oil is China."
China is a historic ally and North Korea's most important trading partner and Pyongyang is thought to be dependent on China for much of its oil supplies.
Earlier on Wednesday, the White House said that Mr Trump spoke to Xi Jinping by telephone, urging him to "use all available levers to convince North Korea to end its provocations and return to the path of denuclearisation".
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