Donald Trump has expressed frustration with China for failing to do more to cut off support to North Korea and exert pressure to curb its nuclear pursuits.
Pyongyang’s intercontinental ballistic missile test this week demonstrated a dangerous new reach for weapons it hopes to top with nuclear warheads one day.
The launch is spurring US demands for global action to counter the threat.
Since he entered the White House, Mr Trump has talked about confronting Pyongyang and pushing China to increase pressure on the North, but neither strategy has produced fast results.
He had expressed optimism after his first meeting with China’s President Xi Jinping that the two would work together to curb North Korea’s nuclear programme, but on Wednesday he condemned China on Twitter.
"Trade between China and North Korea grew almost 40% in the first quarter. So much for China working with us - but we had to give it a try!"
In his initial response to the launch on Monday evening, Mr Trump urged Beijing on Twitter to "put a heavy move on North Korea and end this nonsense once and for all!"
But he also said it was "hard to believe" that South Korea and Japan, the two US treaty allies most at risk from North Korea, would "put up with this much longer".
North Korea conducts about 90% of its trade through China. Beijing has long resisted intensifying economic pressure on neighbouring North Korea, in part out of fear of the instability that could result on its doorstep, and Mr Trump has not found a way to break through Beijing’s old habits.
Mr Trump spoke with Mr Xi and Japanese prime minister Shinzo Abe on Monday, discussing North Korea and its nuclear programme. He will meet them both again this week at the G20 meeting in Germany, as well as have his first meeting with Russian President Vladimir Putin.
US officials joined South Korea and Japan in requesting an emergency meeting of the UN Security Council.