SEOUL, South Korea — South Korea listed 126 Iranian companies and individuals for economic sanctions on Wednesday, including a major Iranian banking operation in Asia, despite Tehran’s warnings that the penalties would endanger South Korea’s growing trade and energy ties with Iran.

The South Korean actions included effectively hamstringing Bank Mellat’s Seoul office, which handles 70 percent of South Korean exports to Iran. The office is the only Asian branch of Iran’s second-largest bank, which the United States has accused of facilitating hundreds of millions of dollars in transactions for Iranian nuclear, missile and defense entities.

Bank Mellat’s Seoul branch will now need to obtain approval from the Bank of Korea, the central bank, before executing any financial deal. South Korean financial regulators also plan to suspend the bank’s operations for an unspecified period — local news outlets said for two months — for assisting Iran’s suspected efforts to develop weapons. Officials here said that wiring money from a third country to Iran through the Bank Mellat in Seoul will be blocked.

…Bilateral trade between Iran and South Korea grew to $9.6 billion last year, up from $2.9 billion in 2001. In the first seven months of the year it rose 53 percent to $7.4 billion — thanks mainly to increased oil exports to South Korea and a growing Iranian appetite for South Korean electronics and vehicles.

South Korean officials said they were talking with Tehran to open accounts based on South Korea’s currency, the won, in the Iranian central bank to help South Korean companies avoid going through European and Japanese banks and to facilitate their oil and other legitimate dealings with Iran.