South Korea is now in a dilemma over what stance it should take as the United States recently asked for its cooperation in toughening sanctions on Iran for its alleged pursuit of nuclear weapons programs, officials and experts said Tuesday.

The request comes after the U.S. and some other countries slapped sanctions on Iran's financial, petrochemical and energy sectors last month following a United Nations report that Tehran is researching nuclear weapons.

Robert Einhorn, the U.S. State Department's special adviser for nonproliferation and arms control, recently visited South Korea, calling for Seoul's cooperation. He also reportedly met with a senior finance ministry official to ask for joining the sanctions, sources said.

"We cannot talk about anything about Iran," a government official here said. "We cannot say whether or not the government is considering any sanctions at this moment, not to mention of any specific measures or timetable."

What measures the U.S. asked for and what action South Korea will take has yet to be confirmed, but the request from its closest ally surely brought the Seoul government into a hot spot as the fallout could be significant given its increasing economic ties with Iran, experts said.

Iran is one of South Korea's major business partners in the Middle East with their bilateral trade volume reaching about US$14.5 billion during the first 10 months of this year. The amount is the highest ever, surpassing the previous annual record of $12.6 billion in 2008.

South Korea has a relatively strong dependence on Iran's oil.

It brought in about 72.6 million barrels of crude oil from the country last year, about 8.3 percent of its total oil imports, according to the Korea National Oil Corp.

South Korea has been expanding its exports to the Middle East country with ships, plants and steel exports making up the largest slice. Passenger cars produced by Korean companies account for about 40-50 percent of imported vehicles in Iran, industry data showed.

Though Washington is not demanding South Korea stop purchasing oil from Iran, Seoul is still in a tight spot as any move to add pressure on the Islamic country could have negative impact on their overall bilateral business relations. But not joining would not be an easy option either considering its age-old ties with the U.S.

"We have maintained relations with Iran relatively well since Seoul imposed sanctions against an Iranian bank last year, but it is yet another quite sticky situation being asked again to take actions against the country," a government official said on condition of anonymity.

South Korea suspended the operation of the Seoul branch of Iran's Bank Mellat for two months from October to December last year at the request of the U.S.

The bank recently filed a lawsuit against the South Korean government for the punitive measure, saying the allegations of illicit transactions are groundless. (Yonhap News)