SEOUL, Sept. 8 (UPI) -- South Korea said Wednesday it is joining a U.S.-led campaign to sanction Iran for its suspected nuclear weapons program.

South Korean Foreign Ministry spokesman Kim Young-sun said his country will penalize a key Iranian bank and put nearly all financial transactions with Iran under government supervision, the Yonhap news agency reported.

The Seoul branch of Iran's Bank Mellat has been accused of facilitating hundreds of millions of dollars in transactions for Iranian nuclear, missile and defense entities.

Kim said the government would give a "heavy penalty" to the bank but declined to elaborate.

The United States has said it wants South Korea to shut down Bank Mellat's Seoul branch instead of suspending its operations.

Kim said all normal and legitimate transactions with Iran would continue.

A senior government officials told Yonhap that South Korea is "in the process of explaining" the sanctions to Iran.