US Treasury Secretary Steven Mnuchin promised to play an important role in cranking up sanctions on North Korea, South Korean Foreign Minister Yun Byung-se Wednesday.

Yun said he met with Mnuchin during a foreign ministers' meeting of 68 countries that the State Department hosted to discuss the fight against the militant group Islamic State.

"Secretary Mnuchin stressed that the Treasury Department will play an important role in North Korea sanctions," Yun told reporters.

Yun said he also met with Defense Secretary James Mattis and Secretary of State Rex Tillerson.

Mattis was quoted as telling Yun that the US will stand by South Korea as it goes through a difficult time. He also reaffirmed the firm US security commitment to the South, Yun said.

Yun also said that South Korea and the US share an understanding on the need for maintaining pressure and sanctions on North Korea, and that consensus is being reflected in the ongoing US review of North Korea policy. South Korea has been conveying its views to the US through Tillerson, Yun said.

On China's retaliation against South Korea for hosting the US THAAD missile defense system, Yun said that Tillerson delivered the US position on the issue to China, just as he stated the position during his press conference in Seoul.

Tillerson called China's retaliation as "inappropriate and troubling" and urged Beijing to "address the threat that makes that necessary, that being the escalating threat from North Korea." (Yonhap)