A senior official from the U.S. Treasury Department on Tuesday begins a mission to Japan and South Korea to press for implementation of international sanctions against Iran.

According to a Treasury Department statement, Undersecretary David Cohen will consult with officials in the two countries on steps to increase pressure on what were described as “those entities facilitating Iran's illicit activities,” including Iran's Islamic Revolutionary Guard.

The United States, joined by the United Nations International Atomic Energy Agency, has long accused Iran of seeking to acquire low-enriched uranium that can be used to make nuclear weapons.

Iran insists its nuclear program is for peaceful purposes.