Iranian supplies 10 percent of South Korea's oil imports.
U.S. State Department's special adviser for non-proliferation and arms control, Robert Einhorn, who arrived in Seoul Monday, assured Washington would help South Korea minimize any fallout from the sanctions, Yonhap News agency reported.
Einhorn, who held talks with South Korean Deputy Foreign Minister Kim Jae-Shin earlier Tuesday, said, "We are urging all of our partners to help us, work with us in putting more pressure on the government of Iran to get them to negotiate seriously.
"In particular, we are urging them to reduce their purchases of crude oil from Iran and we are urging them to unwind their financial dealings with the Central Bank of Iran."
Einhorn stressed the U.S. policy would be implemented "while maintaining stability of international oil markets," adding "we want to do this while being very sensitive to the economic interests of our close allies like (South Korea) and South Korean companies," Yonhap reported.
Under a U.S. law signed by President Barack Obama, there would be sanctions against financial institutions dealing with Iran's central bank.
The South Korean deputy foreign minister was quoted as saying his country is "committed to strongly supporting and participating in international efforts to resolve this issue" but expressed concerns about the impact of cuts in Iranian oil purchases on the South Korean economy.