U.S. President Donald Trump expressed disappointment in an early morning tweet that a Chinese envoy's recent visit to Pyongyang appeared to have had "no impact" on stopping such provocations.

"I think the Chinese are doing a lot," Tillerson told reporters when asked if he shares the president's sentiment. "We do think they could do more with the oil, and we're really asking them to please restrain more of the oil -- not cut it off completely."

China is known to be reluctant to exert any kind of pressure that could cripple the North Korean regime and spark instability on their shared border.

"That was the most effective tool the last time the North Koreans came to the table, was cutting the oil off," Tillerson said, referring to the denuclearization talks that began after China suspended its oil supply in 2003.

Those negotiations fell through in 2008.

Pyongyang has vowed to build a nuclear-tipped missile capable of hitting the U.S. to deter what it sees as Washington's hostility. (Yonhap)