A senior U.S. diplomat on Tuesday asked South Korea to reduce imports of Iranian crude oil in support of U.S. sanctions that punish Tehran for its nuclear program.

The U.S. State Department’s adviser for non-proliferation and arms control, Robert Einhorn, also urged Seoul to cut back its business ties with Iran’s central bank.

“We’re urging all our partners to consider what they can do to reduce imports of crude oil from Iran as well as to unwind overtime their relationships with the central bank of Iran.”

Einhorn arrived in Seoul Monday for a three-day visit. He is trying to gain support for recently enacted U.S. legislation that imposes tough financial measures against institutions that do business with Iran’s central bank. Washington hopes the sanctions will pressure Iran to abandon its nuclear program, which the U.S. suspects is being used to produce weapons.

South Korean Deputy Foreign Minister Kim Jae-shin said he strongly supports international efforts to resolve the Iranian nuclear issue. But he said many in South Korea are concerned that the economic sanctions could hurt his country’s economy.

“Many in South Korea are quite worried that further strengthening sanctions against Iran at this time may destabilize international markets of crude oil and accordingly bring about some adverse affects on the Korean economy, as well.”

South Korea – a key U.S. ally – gets about 10 percent of its oil imports from Iran, and many in South Korea are concerned that the sanctions may drive up the price of oil.

But Einhorn said he believes the U.S. can put pressure on Iran while maintaining the stability of the international oil market.

The issue has proved politically controversial for the government of South Korean President Lee Myung-bak. Outside the Foreign Ministry Tuesday, a small group of protesters chanted anti-U.S. slogans urging Seoul to not join the Iran sanctions.

“If the Lee Myung-bak government submits to pressure by the United States and joins the Iran sanctions, it will effect our economy badly. Therefore, we urge the Lee Myung-bak government to resist the pressure and proudly protect our sovereignty”

Einhorn is expected to meet later Tuesday with South Korean Energy and Finance Ministry officials.

U.S. officials are in the beginning stages of an effort to lobby for international support for the sanctions against Iran.

Last week, U.S. Treasury Secretary Timothy Geithner met with officials in Japan and China, to mixed results. While Japan’s finance minister promised to take steps to reduce Iranian oil imports, Chinese officials did not give any sign they would comply with the sanctions.

Iran denies that its nuclear program is aimed at producing weapons, insisting that it is for producing electricity and medical isotopes to treat cancer patients.