It was the government's own decision to impose the "unilateral" sanctions, and the measures are based on the existing UN resolution, the official added, apparently downplaying Washington' s role in prodding Seoul into action.
Despite the government's efforts to "minimize damage" the sanctions might bring about, concerns still linger over worsening financial ties with Iran.
Seoul relies on Tehran, the biggest trade partner in the Middle East, for 10 percent of its crude oil imports. Some 2,000 small and mid-sized enterprises have tapped into the fast-growing Iranian market.
Still, the government will maintain "legitimate" trade relations and exchanges with Iran, and will take measures to support domestic small and mid-sized firms, foreign ministry spokesman Kim Young-sun told reporters. Seoul's oil imports from Tehran will not be affected by sanctions, another official said.