US President Donald Trump has said that "the Chinese envoy, who just returned from North Korea, seems to have had no impact on Little Rocket Man," in reference to leader Kim Jong-un.
Mr Trump's comments come on the heels of North Korea's latest missile launch.
China had dispatched the envoy earlier in the month after Mr Trump travelled to China on his recent 12-day Asia tour and met with Chinese President Xi Jinping.
"It is a situation that we will handle," Mr Trump told reporters just after the missile launch.
The next morning the President announced new sanctions against the isolation Korean peninsula nation.
Pressure on North Korea's economic allies like China, Russia, and southeast Asian nations is also mounting.
The US Ambassador the United Nations Nikki Haley once again called on China to step up its support of sanctioning Pyongyang.
The neighbours have long been oil suppliers to North Korea, fuelling its economy.
Ms Haley, at a meeting of the UN Security Council said: "We have never sought war with North Korea, and still today we do not seek it...if war comes, make no mistake, the North Korean regime will be utterly destroyed."
This is the first test the hermit kingdom has conducted in two months, its 20th overall, and its seventh actual launch of a weapon. On 15 September North Korean leader Kim Jong-unlaunched an intermediate ballistic missile over the coast of Hokkaido island in northern Japan which landed in the Pacific Ocean.
South Korea's military says the missile was fired from an area north of Pyongyang early on Wednesday morning local time.
The Pentagon tracked the trajectory of the weapon and spokesman Colonel Rob Manning said the missile was launched from Sain Ni, North Korea, and travelled about 620 miles (1,000 km) before landing in the Sea of Japan.
It also reportedly went approximately 2,800 miles (4,000 km) up into the atmosphere, according to South Korean and Japanese authorities. US Defence Secretary James Mattis said the latest missile did fly higher than previous ones.
He warned that North Korea continues to strengthen its nuclear weapons programme with weapons that "threaten everywhere in the world."
The US also just declared North Korea a state sponsor of terrorism, saying acts like the assassination of Mr Kim's half brother Kim Jong-nam in Macao contributed to the designation.
Secretary of State Rex Tillerson called the move as "very symbolic...practical effects may be limited but hopefully clos[es] off loopholes" in existing sanctions for "dual use" product exports that can be used by civilian and military end-users within North Korea.
Those products require separate licenses to sell under US export regulations.
North Korea was last on the state-sponsored terror list in 2008, under the George W Bush administration. It was removed that year in a bid to salvage a deal halting its nuclear development.
Mr Tillerson said that attempt at negotiations "obviously failed."
He noted that North Korea's fuel supply "is already quite constrained" as shown by "anecdotal evidence" and US intelligence sources which show cars lined up at petrol stations or certain stations closing that would normally have fuel.
The issue there is that the country only has one refinery that operates internally so they are heavily reliant on finished fuel imports.
The state news agency released photos of Mr Kim celebrating the recent missile launch after experts said Pyongyang may have the capability to strike the US mainland.
Mr Kim described the act as a “breakthrough” in a statement read by a television news presenter.
