South Korea's trade with Iran has dropped more than 20% this year due to the resumption of US sanctions.
And more losses are likely when the sanctions are strengthened next month, the Yonhap news agency reported.
Export figures to the end of August from the Korea International Trade Association (KITA) totalled $2.08bn, down 21.9% from 2017.
Imports were $4.05bn, a fall of 23.7%.
